Find the program that prints this integer sequence (Cops' thread)

• The cop's task is to write a program/function that takes a positive (or non-negative) integer and outputs/returns another integer.
• The cop must state it if the program is intolerant towards zero.
• The cop will provide at least 2 sample inputs/outputs.
• For example, if I have decided to write the Fibonacci sequence, I would write this in my answer:
a(0) returns 0
a(3) returns 2

• The number of examples is up to the cop's discretion.
• However, the sequence must actually exist in the On-Line Encyclopedia of Integer Sequences®, so no pseudo-random number generator for you. :(
• The cop can hide as many characters as is so wished.
• For example, if my program is:

function a(n)
if n>2 then
return n
else
return a(n-1) + a(n-2)
end
end


• Then I would hide these characters as I want:

function a(n)
if ### then
########
else
######################
end
end


• is obviously to find the original source code.
• However, any proposed source code that produces the same set of output also counts as valid, as long as it is also found in OEIS.

Tips for the cops

• The search function in the OEIS only works for consecutive terms, so if you want to hide your sequence, then just leave a hole anywhere.
• Apparently there is no way to hide the sequence. Put this in mind when you choose the sequence.

The winner will be the submission with the lowest score that hasn't been cracked in 7 days.

Only submissions that are posted in 2016 April are eligible for the win. Submissions that are posted later than this are welcome, but cannot win.

In order to claim the win you need to reveal the full code and the OEIS sequence (after 7 days).

Your post should be formatted like this (NN is the number of characters):

Lua, 98 bytes

Output:

a(0) returns 0
a(3) returns 2


Code (# marks unrevealed characters):

function a(n)
if ### then
########
else
######################
end
end


If the code is cracked, insert [Cracked](link to cracker) in the header. If the submission is safe, insert "Safe" in the header and reveal the full code in your answer. Only answers that have revealed the full code will be eligible for the win.

• Also, OEIS search can have blanks with _, fyi – Sp3000 Apr 9 '16 at 0:59
• It may be too late to change, but allowing sequences that are multiples of an OEIS sequence, and/or only include every nth term would have made this challenge much better. sandbox, hint, hint – Nathan Merrill Apr 9 '16 at 2:37
• Can I, for example, pick the Fibonacci sequence and provide only a(1000)? (which is part of the sequence, but too large to be searchable on OEIS) – Sp3000 Apr 9 '16 at 6:36
• I'd say the values have to actually be searchable on OEIS, so that it can easily be verified that the values are correct for the chosen sequence. – user45941 Apr 9 '16 at 6:38
• "Intolerant towards zero" makes no sense. What is that supposed to mean? – feersum Apr 10 '16 at 23:28

i****<esc>:let @q="^*i****$**@***"<cr><n>@qbD  (Note: <n> is where you type your input) Here is the code unrelated to number generation:  :let @q=" "<cr><n>@qbD  Meaning I am revealing 5 out of 19 characters. <n> is the input. Here are some sample outputs: 1@q: 1 2@q: 3 6@q: 18  Answer This code prints The Lucas Numbers (A000032), which are just like The Fibonnaci Sequence, except that it starts on 2, 1 instead of 1, 1. Here are the first 15 numbers: 2, 1, 3, 4, 7, 11, 18, 29, 47, 76, 123, 199, 322, 521, 843  Here's the revealed code: i2 1 <esc>:let @q="^diwwyw$pb@-<c-v><c-a>"<cr><n>@qbD


Explanation:

i2 1 <esc>                          "Insert the starting numbers
:let @q="....."<cr>       "Define the macro 'Q'


Explanation of the macro:

^                      "Move to the first non-whitespace character on the line.
diw                   "(d)elete (i)nner (w)ord. This is different then 'dw' because it doesn't grab the space.
"It also throws people off since 'i' is usually used for inserting text.
wyw$"Move to the next number, yank it then move to the end of the line pb "(p)aste the yanked text and move (b)ack @- <c-a> "@- is the register holding the word we deleted. Increment the current number that many times. <c-v> "Since we're adding <c-a> this from the command line, we need to type it as a literal.  Now, we just need to remove the second number, since the first number is the lucas number we want. So we do b "move (b)ack D "(D)elete to the end of the line.  Also, if I'm not mistaken, this is the first safe submission! That's kinda cool. • I know the sequence, I think. I just don't know how to turn it into Vim keystrokes. – Fund Monica's Lawsuit Apr 9 '16 at 6:54 • Is the output just the number or the entire line? – ASCIIThenANSI Apr 11 '16 at 20:51 • @ASCIIThenANSI After hitting bD at the end, the output is just the one number and some extra whitespace. – DJMcMayhem Apr 11 '16 at 20:58 • I got the sequence right! – Fund Monica's Lawsuit Apr 16 '16 at 4:58 05AB1E, 5 bytes, safe Last one for today :p. Output: a(0) = 9 a(5) = 4 a(10) = 89  Code: ___m_  Obfuscated characters are indicated with _. Try it online!-link. Uses CP-1252 encoding. Solution: žhžm‡  Explanation: žh # Short for [0-9]. žm # Short for [9-0]. ‡ # Translate.  • I know the sequence, just not how to generate it in so few bytes... – LegionMammal978 Apr 9 '16 at 20:26 • @LegionMammal978 Yes, I think that is going to be the hardest part of this one. – Adnan Apr 9 '16 at 20:57 • I can get it in 5 bytes with g°<¹- but I can't figure out any way to use m at this size! D: – user81655 Apr 11 '16 at 0:42 • @user81655 Yes, that was the alternative solution :). – Adnan Apr 11 '16 at 4:39 Element, 7 bytes, cracked Output: a(3) = 111 a(7) = 1111111  The # are hidden characters, and they are all printable ASCII. I think this one is actually reasonably difficult (for only having 5 missing characters). ###,##}  For convenience, here's the Try It Online and Esolang wiki pages. My original program was: _'[,$}

The trick is that

] and } are functionally identical (both translate to } in Perl). Also, I used ,$ to produce a 1 as an additional layer of confusion, although it is possible to ignore the , completely by doing ,1 instead. • (I know I shouldn't ask this, but) are you sure that it is correct? In particular, } instead of ]? – Leaky Nun Apr 9 '16 at 5:18 • @KennyLau The } is correct, and my program (as far as I know) works in every version of Element. – PhiNotPi Apr 9 '16 at 5:20 • Cracked. – Leaky Nun Apr 9 '16 at 6:07 • I think the formatting is wrong in your original code? – Rɪᴋᴇʀ Apr 9 '16 at 21:46 • @EasterlyIrk It is. If you know how to fix it, be my guest. – PhiNotPi Apr 9 '16 at 21:55 Jolf, 5 bytes, cracked Output: a(2) = 8 a(10) = 4738245926336  All of it is crucial, and I have shown 1 of 5. ####x  Original code: mPm$x
mP     cube
m$catalan number x input  Try it online! • Cracked! – Leaky Nun Apr 9 '16 at 1:33 • For anyone interested, it's this sequence: oeis.org/A033536 – Blue Apr 9 '16 at 1:34 JavaScript (ES7), 10 bytes, Cracked Output f(0) -> 1 f(1) -> -1  Code t=>~t##**#  Test it in Firefox nightly. The code is an anonymous function. This will probably be easy since there's only three characters hidden, but at least it's short! :P My original code was: t=>~top**t but after brute-forcing my own code for a solution, I soon realised t=>~t.x**t (where x can be any variable name character) could also be used. This works because in the original ES7 exponentiation operator spec, the operator had lower precedence than unary operators (unlike conventional mathematics and most other languages). ~ performs a bitwise NOT on t.x (undefined) or top (Object) which casts them to a 32-bit signed integer (uncastables like these become 0) before doing the NOT (so 0 becomes -1). I looked into further into this, and very recently, the spec has changed to disallow ambiguous references like this (not good for future golfing D: ), however most ES7 engines haven't updated to the latest version of the spec yet. • @insertusernamehere It seems to think it contains an illegal expression. It does work in Firefox nightly though. I guess they implement the ES7 spec differently. – user81655 Apr 13 '16 at 9:33 • I just got Firefox nightly, and I must complain that this does not work there. 32-bit windows from here – Conor O'Brien Apr 13 '16 at 21:11 • Assuming ** is equivalent to Math.pow, I have done some of my own testing, and even run a brute force. This is quite hard to crack! – Conor O'Brien Apr 13 '16 at 21:42 • @CᴏɴᴏʀO'Bʀɪᴇɴ My Firefox nightly is up to date as of yesterday. I'm using OS X but I'm quite sure it will work in Windows also. Traceur with appropriate ES7 options enabled transpiles it correctly too. – user81655 Apr 13 '16 at 22:30 • @CᴏɴᴏʀO'Bʀɪᴇɴ Just tried it in 32-bit Windows from your link and it works also. I'm surprised your brute force search couldn't crack it. I actually just realised there's many solutions to this! D: – user81655 Apr 13 '16 at 23:40 05AB1E, 4 bytes (Cracked) Sample output : a(5) = 51 a(8) = 257  And for the code : ###^  I revealed the last one. Should be easy enough though, I had quite a hard time finding a sequence :( All hidden characters are printable. • Cracked! :) – Adnan Apr 9 '16 at 9:32 MATL, 5 bytes, cracked Hidden characters are indicated by %. %5%*%  Output: a(1) = 3 a(2) = 6 a(4) = 12  Input 0 is valid. Original code: 35B*s  that is, 35 % push number 35 B % convert to binary: array [1 0 0 0 1 1] * % multiply element-wise by implicit input n: gives [n 0 0 0 n n] s % sum of array: gives 3*n  • Hmmm, the five in code is very annoying! – Adnan Apr 9 '16 at 12:27 • Technically this could be brute-forced by a program... but I won't do that. – Leaky Nun Apr 9 '16 at 12:37 • cracked – flawr Apr 9 '16 at 19:19 SWIFT, 55 bytes, Cracked func M(n:Int)->Int{ return(n*****) ?M(**n****):n***; }  * marks a hidden character Output: M(30) -> 91 M(60) -> 91 M(90) -> 91 M(120)-> 110 M(150)-> 140  Function accepts 0 • Cracked – Emigna Apr 14 '16 at 9:45 Ruby, 46 bytes, safe Edit to add disclaimer/apology: This sequence starts with f[0], while the OEIS entry starts with f[1]. The values are the same. Obfuscated code (# is any character): ->####or x##1###(#..##0#);x*=3;end;#.###ect:+}  Call like ->####or x##1###(#..##0#);x*=3;end;#.###ect:+}[3] (returns 39)  Output: f[0] = 0 f[1] = 3 f[2] = 12 f[3] = 39 f[4] = 120 f[5] = 363 f[6] = 1092 f[7] = 3279 f[8] = 9840 f[9] = 29523  Solution: f=->*x{for x[-1]in(0..x[0]);x*=3;end;x.inject:+} Sequence: Explanation: The minor trick here is that we declare the parameter as *x rather than x. This means that if you pass in 2, x is set to [2]...at first. The major trick exploits bizarre, and justly obscure, Ruby syntax where you can set the iterator in a for loop to any valid left hand side of an assignment expression, instead of an iterator variable like i. So this loops through from 0 to (in this example) 2, assigning each number to x[-1], meaning it overwrites the last value of x. Then the loop body x*=3, further mutates x by concatenating it to itself 3 times. So first x becomes [0], then [0,0,0]. On the next loop it becomes [0,0,1], then [0,0,1,0,0,1,0,0,1]. Finally we pass in 2 and it becomes [0,0,1,0,0,1,0,0,2], then [0, 0, 1, 0, 0, 1, 0, 0, 2, 0, 0, 1, 0, 0, 1, 0, 0, 2, 0, 0, 1, 0, 0, 1, 0, 0, 2]. We then sum the result using the inject method, which reduces the array by applying + (the passed in method) to each element in turn. If we consider how each iteration changes the sum, we see that we effectively add 1 (by overwriting the last element with an element one higher), then multiply by 3. Since 3*(n+1) = 3*n + 3, this implements Alexandre Wajnberg's recurrence relation for the sequence as described on the page. • I really like your cops here, this one particularly. Well done. – Not that Charles Apr 13 '16 at 14:27 05AB1E, 3 bytes, cracked Output: a(9) = 165 a(10) = 220  Hidden code: ##O  Try it online might come in handy. Hexagony, 7 bytes, cracked Output: a(1) = 2 a(2) = 4  Hidden code: ?#####@  Or alternatively:  ? # # # # # @  Try it online might come in handy. • Cracked. – Martin Ender Apr 9 '16 at 8:42 • Uhhh wait, does your code work for input 0? – Martin Ender Apr 9 '16 at 8:44 • @MartinBüttner Oh, it doesn't, my bad. Your solution was the right one though. – Adnan Apr 9 '16 at 9:03 PHP, 41 bytes, cracked Yeah, finally another Cops and Robbers challenge. Hope I didn't make it to easy. Output a(5) = 0 a(15) = 1 a(35) = 0 a(36) = 1 a(45) = 1  Source ____________________$argv[1]____________;
####################        ############


Notes

Cracked

I obviously made it to easy and provided not enough examples. The sequence I had in mind was A010054:

a(n) = 1 if n is a triangular number else 0.

Here's my original source code:

echo(int)($r=sqrt(8*$argv[1]+1))==$r?1:0; It tests whether the input is a triangular number and outputs 1 or 0 accordingly. Jolf, 11 bytes, Cracked , A011551 c*______x__ c*mf^+91x~P  Original code: c*^c"10"x~P  Examples: 0 -> 1 12 -> 1618033988749  • – Adnan Apr 9 '16 at 22:07 • @Adnan Good job, though different from mine. And you couldn't figure out first op. :P – Rɪᴋᴇʀ Apr 9 '16 at 22:17 • Yeah, I couldn't figure out what it does :p – Adnan Apr 9 '16 at 22:30 • @Adnan it was a cast to int function, misused as a floor one. – Rɪᴋᴇʀ Apr 9 '16 at 23:02 MATL, 9 bytes, Cracked Code: 3#2###*##  Output: a(1) = 3 a(2) = 6 a(4) = 12 a(12) = 37  a(0) is valid. Cracked Original sequence: A059563 Original code: 3L2^Ze*sk 3L % Push [1 -1j] from the clipboard 2^ % square Ze % exp * % times input s % sum k % floor  • – Adnan Apr 9 '16 at 22:55 Java, 479 bytes, Cracked Outputs: a(10) = 81 a(20) = 35890  (Inputs are provided via command line arguments) Code (# marks hidden characters): import java.util.*; public class A{ public static int######### public boolean########### static A a = new A(); public static void main(String[] args){ int input = Integer.parseInt(args[0]); LinkedList<Integer> l = new LinkedList<>(); l.add(1); l.add(0); l.add(0); for(int ix = 0; ################if(##>##{ ###########d# #######+##p##########+##########(####### } System.out.println(######################### ###(A.#############(#5#####))); } }  The program starts at index 0. (Note that SE replaces all of the \t indents with 4 spaces, bringing the byte total to 569. Click here to see the program with \t indents instead of space indents.) Original code: import java.util.*; public class A{ public static interface B{ public boolean C(int i);} static A a = new A(); public static void main(String[] args){ int input = Integer.parseInt(args[0]); LinkedList<Integer> l = new LinkedList<>(); l.add(1); l.add(0); l.add(0); for(int ix = 0; ix<input; ix++)cif(i-> { return l.add( l.pop()+l.peekFirst()+l.peekLast());});{ } System.out.println(l.get(1));}static boolean cif(A.B b5){return (b5.C((0))); } }  (Same code, but formatted normally): import java.util.*; public class A { public static interface B { //functional interface for lambda expression public boolean C(int i); //void would have given it away } static A a = new A(); //distraction public static void main(String[] args) { int input = Integer.parseInt(args[0]);//Input LinkedList<Integer> l = new LinkedList<>(); l.add(1);//Set up list l.add(0); l.add(0); for (int ix = 0; ix < input; ix++) cif(i -> { //Fake if statement is really a lambda expression return l.add(l.pop() + l.peekFirst() + l.peekLast()); }); { //Distraction } System.out.println(l.get(1));//Output } static boolean cif(A.B b5) { //Used to pass in lambda expression. //The A. and b5 were both distractions return (b5.C((0))); } }  • Hm, how do you come to a byte count of 488? I count 545 from i to }? And please specify 0-tolerance. – Vampire Apr 9 '16 at 23:46 • Aren't your examples a(9) and a(19) or a(8) and a(18), according to which version of it on OEIS you took? – Vampire Apr 9 '16 at 23:54 • @BjörnKautler I'll post a link to the byte counter when I get home. What do you mean by 0-tolerance? The first value is a(1) = 0 – Daniel M. Apr 9 '16 at 23:55 • From the OP: "The cop's task is to write a program/function that takes a positive (or non-negative) integer and outputs/returns another integer. The cop must state it if the program is intolerant towards zero." So I guess you take the input 1 as 0 and this also explains the shift in position, according to the OEIS sequence. – Vampire Apr 9 '16 at 23:58 • @BjörnKautler OK, thanks. The program doesn't crash if 0 is entered but the sequence starts at index 1, so I guess it's zero-intolerant. – Daniel M. Apr 10 '16 at 0:02 Octave, 34 bytes, cracked @(m)(m###m#####m##)&isprime(#)####  Outputs: ans(1) = 0 ans(6) = 5 ans(7) = 10 ans(8) = 15  The sequence starts at ans(1) in OEIS. C, 71 bytes cracked ############ ##### main(){ scanf("%d",##); ###6#; printf("%d",##); }  Output: a(1) = 0 a(2) = 0 a(5) = 1 a(6) = 1 a(7) = 1 a(9) = 2  This works with gcc, and is a full program. It accepts 0 as input. Pyth, 70 bytes, Cracked DhbI|qb"#"qb"#"R!1Iqb"#"#####+""s####2###;##lY+Q1Ih+""Z#####)=Z+Z1;@YQ  # are the hidden characters Has been cracked, so here is the versionn without hidden chars : DhbI|qb"4"qb"0"R!1Iqb"1"R!0Rh+""sm^sd2cb1;W<lY+Q1Ih+""Z=Y+YZ)=Z+Z1;@YQ  Sample outputs : a(2) -> 10 a(4) -> 19  Good luck to find this on OEIS, I personally failed to find it from those examples (even tho the sequence is quite easy to spot.) • – Adnan Apr 10 '16 at 19:39 Ruby, 38 bytes, cracked Obfuscated code (# can be any character): ->#{(s=#########).sum==#3333&&eval(s)}  Output: Multiplies the input by 10 (A008592). Works for any integer, including 0. e.g. ->#{(s=#########).sum==#3333&&eval(s)}[3] => 30 ->#{(s=#########).sum==#3333&&eval(s)}[10] => 100  • Cracked. – xsot Apr 12 '16 at 6:40 05AB1E, 5 bytes, cracked Output: a(0) = 0 a(1) = 0 a(2) = 1 a(3) = 1 a(4) = 1 a(5) = 1 a(6) = 1 a(7) = 1 a(8) = 1 a(9) = 1 a(10) = 0 a(11) = 0  Obfuscated code: _____  Try it online!-link. 05AB1E, 4 bytes, cracked Well then, I think I'm addicted to CnR's... Obfuscated code (_ indicates a wild card): ____  Sequence: a(1) = 2 a(4) = 6720  The sequence in OEIS starts at a(1) = 2. Try it online!-link • Cracked – David Apr 13 '16 at 4:28 Lua, 45 Bytes, Cracked A small hint: a(0) will make the program crash :)  Output a(1)=>0 a(2)=>1  Code Uses # to hide the code :). a=function(n)#####n###### and #or ########end  I was using the OEIS A007814, with the following code: a=function(n)return n%2>0 and 0or 1+a(n/2)end  • – Leaky Nun Apr 14 '16 at 9:36 • @KennyLau Well done, I've added the OEIS I was thinking to and the intended code, I should have added at least one more output to prevent this to happen :p – Katenkyo Apr 14 '16 at 9:42 Pyke, 15 bytes, SAFE Output a(2) = 21 a(15) = 17  Revealed code: #R#D######+##)#  Solution: OEIS A038822 wR}DSR_Q*L+#P)l I used a couple of red herrings here by using wR} to generate the number 100 and revealing the character R which is normally used to rotate the stack. I also used #P)l instead of the more simple mPs to count the number of primes in the sequence. • The sequence in question starts from n=1 not n=0 by the way – Blue Apr 9 '16 at 11:09 • I thought it was that sequence, except it starts at n=0 and not n=1 as you've stated. – Emigna Apr 18 '16 at 11:07 C, 82 bytes, safe ####=############ main(i){scanf("%d",##); for(i=1;i++/4<#;)##=2; printf("%d",##);}  Works with gcc, and it is a full program, which reads its input from stdin and prints its output to stdout. Here the sequence is A004526, floor(n/2). a(0) = 0 a(1) = 0 a(2) = 1 a(3) = 1 a(4) = 2 a(5) = 2 a(6) = 3 a(7) = 3 a(8) = 4  Solution: a;*b=(char*)&a+1; main(i){scanf("%d",&a); for(i=1;i++/4<2;)a*=2; printf("%d",*b);}  This works only on little endian machines, and only if the size of char is 1 byte. And only if the byte higher than the highest order byte of a has value 0. I think this is true for gcc since by default uninitialized global variables go into the bss segment, and initialized global variables go into the data segment (see https://stackoverflow.com/questions/8721475/if-a-global-variable-is-initialized-to-0-will-it-go-to-bss). So only a goes into bss (the only other global variable b is initialized and thus goes into the data segment). If a is not at the end of bss, then the byte higher than the highest order byte of a is also in bss and thus has value 0. • Try making function calls now :) – mIllIbyte Apr 11 '16 at 11:22 • I don't think you had to specify the sequence... – FliiFe Apr 11 '16 at 13:35 • @FliiFe - Fixed :) – mIllIbyte Apr 11 '16 at 13:39 05AB1E, 1 byte, Cracked _  _ denotes hidden code. f(1) == 1 f(18) == 6  • Cracked – Emigna Apr 27 '16 at 6:11 Element, 10 bytes, cracked Output: a(3) = 6561 a(4) = 4294967296  There's probably only a few ways to compute this sequence in Element. I found a 9-char solution, but I figured this 10-char solution is actually more difficult. The # are hidden characters. #_####@^#  For convenience, here's the Try It Online and Esolang wiki pages. The original was 2_3:~2@^^  • Show one more byte. – Leaky Nun Apr 9 '16 at 3:02 • @KennyLau I thought it was 1 out of 5? It's 10 bytes and I'm showing 3. – PhiNotPi Apr 9 '16 at 3:03 • Inputs and outputs don't count, so you have 8 bytes and you showed 1. – Leaky Nun Apr 9 '16 at 3:07 • @KennyLau done. – PhiNotPi Apr 9 '16 at 3:09 • Cracked. – Leaky Nun Apr 9 '16 at 3:20 Pyth, 18 bytes # marks unrevealed characters. L?Jtb##5#m##S#2 #y  Outputs (starts from 1): 1 -> 2 2 -> 3 3 -> 5 4 -> 7  Online interpreter • Primes, no? If not... – Blue Apr 9 '16 at 12:45 • If not... what? – Leaky Nun Apr 9 '16 at 12:47 • then I have no idea – Blue Apr 9 '16 at 12:47 05AB1E, 5 bytes, cracked I hope that this submission isn't as easy as my other ones :p. Outputs: a(0) = 0 a(1) = 1 a(2) = 6 a(3) = 24 a(4) = 80 a(5) = 240  Obfuscated code: ####O  Contains some non-ASCII characters though, uses CP-1252 encoding. Try it online! might come in handy :p. • Cracked. – LegionMammal978 Apr 9 '16 at 15:12 • Why do I feel like I've seen it before? – Leaky Nun Apr 9 '16 at 16:14 • @KennyLau ¯\_(ツ)_/¯ – Adnan Apr 9 '16 at 16:18 Jolf, 11 bytes, Cracked. Output: a(10) = 4 a(20) = 6 a(30) = 8  And the partially hidden code: ####xd###x#  Hint: When I looked through the sequences in order, I didn't go very far before finding this one. The cracked version isn't quite the same as my original code. I'm not currently at my computer, so I don't have it exactly, but it was something like this: l fzxd!m%xH (The only part I'm unsure about is the !m. It's whatever checks if a variable is zero.) • I found the sequence... Pity I don't know Jolf or javascript very well :( – Blue Apr 9 '16 at 10:57 • @muddyfish, Same here... – LegionMammal978 Apr 9 '16 at 11:00 • Well, I guess it's time for the master to do it... may I? – Conor O'Brien Apr 9 '16 at 14:31 • @CᴏɴᴏʀO'Bʀɪᴇɴ If everyone else is stumped – and it looks like they are – feel free. – Fund Monica's Lawsuit Apr 9 '16 at 14:32 • – Conor O'Brien Apr 9 '16 at 14:35 Pyke, 6 bytes, Cracked ###X#s  Output: a(2) = 8 a(8) = 80 a(10) = 120  This doesn't work with N<1 Original solution: hSmX$s`

• Welp, I found an easier alternate to what I had – Blue Apr 9 '16 at 19:12
• Cracked. – LegionMammal978 Apr 9 '16 at 19:19