Divisibility Streak

We can define the Divisibility Streak k of a number n by finding the smallest non-negative integer k such that n+k is not divisible by k+1.

Challenge

In your language of choice, write a program or function that outputs or returns the Divisibility Streak of your input.

Examples:

n=13:
13 is divisible by 1
14 is divisible by 2
15 is divisible by 3
16 is divisible by 4
17 is not divisible by 5


The Divisibilty Streak of 13 is 4

n=120:
120 is divisible by 1
121 is not divisible by 2


The Divisibilty Streak of 120 is 1

Test Cases:

n      DS
2      1
3      2
4      1
5      2
6      1
7      3
8      1
9      2
10     1
2521   10


More test cases can be found here.

Rules

• You can assume the input is greater than 1.

Scoring

:The submission with the lowest score wins.

• I suggest changing "smallest positive integer" to "smallest nonnegative integer". It doesn't change the challenge at all, but with the current description, it implies we don't need to check for divisibility by 1 (which we technically shouldn't need to). Either that, or you could remove the divisibility by 1 checks from the description. Aug 14, 2017 at 15:11
• The smallest positive integer is 1, and k + 1 is 2, where k is the smallest positive integer. Sorry for the nitpick. Aug 14, 2017 at 15:33
• Isn't this the same as finding the smallest k which doesn't divide n-1? Aug 14, 2017 at 22:28
• @PaŭloEbermann Take n=7 where k=3: n-1 is divisible by k. Aug 15, 2017 at 0:19
• Ah, I missed the +1. Aug 15, 2017 at 16:57

Mathematica, 40 bytes

Min@Complement[Range@#,Divisors[#-1]-1]&


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Mathematical approach, n+k is divisible by k+1 if and only if n-1 is divisible by k+1. And n-1 is not divisible by n, so Range@# is enough numbers.

Originally I intend to use Min@Complement[Range@#,Divisors[#-1]]-1&, but this also work.

• Why does the captcha appear when I use the submission from tio? Aug 14, 2017 at 14:57
• Because you typed (copied-and-pasted) it too quickly. It isn't about TIO. Aug 14, 2017 at 14:58

Julia 0.6.0 (47 bytes) (38 bytes)

n->(i=1;while isinteger(n/i) i+=1;n+=1 end;i-1)

n->(i=1;while n%i<1 i+=1;n+=1end;i-1)

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9 bytes were cut thanks to Mr.Xcoder

• Normally a "Try it online" link allows people to actually try the code by defining some combination of header, footer, and arguments which mean that pressing the play button gives output. Aug 14, 2017 at 15:43
• @PeterTaylor By a pure guess, I tried running it as such, and to my surprise it worked. I recommend the OP to edit in with the testable version. Aug 14, 2017 at 15:55
• 46 bytes (removing one space): n->(i=1;while isinteger(n/i) i+=1;n+=1end;i-1) Aug 14, 2017 at 15:59
• Another pure guess allowed be to golf it down to 38 bytes: n->(i=1;while n%i<1 i+=1;n+=1end;i-1) Aug 14, 2017 at 16:03
• @PeterTaylor Sorry forgot it! Aug 14, 2017 at 17:08

C (gcc), 34 bytes

i;f(n){for(i=1;++n%++i<1;);n=i-1;}


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• Suggest i-- instead of n=i-1 Dec 31, 2018 at 6:02

Batch, 70 bytes

@set/an=%1-1,i=0
:l
@set/ai+=1,r=n%%~i
@if %r%==0 goto l
@echo %i%


All this is doing is finding the largest i such that LCM(1..i) divides n-1.

Aceto, 28 27 bytes

[;%
I)@]
iIk2I(D(
rk[(&Xpu


I could save one byte if I don't have to exit.

Explanation:

We use three stacks: The left stack holds a counter starting at 2, the right one holds the given number (or its increments), the center stack is used for doing the modulo operations. We could, of course, do everything in one stack, but this way we can set the outer stacks to be "sticky" (values that are popped aren't really removed) and save ourselves many duplication operations. Here's the method in detail:

Read an integer, increment it, make the current stack sticky, and "move" it (and ourselves) to the stack to the left:

iI
rk[


Go one more stack to the left, push a literal 2, make this stack sticky, too. Remember this position in the code (@), and "move" a value and ourselves to the center stack again.

  @]
k2
(


Now we test: Is the modulo of the top two numbers not 0? If so, jump to the end, otherwise go one stack to the right, increment, and push the value and us to the middle. Then go to the left stack, increment it, too, and jump back to the mark that we set before.

[;%
I)
I(
&


When the result of the modulo was not zero, we invert the position the IP is moving, go one stack to the left (where our counter lives), decrement it, and print the value, then exit.

      D(
Xpu


F#, 86 bytes 84 bytes

let s n =
let rec c n1 d r=if n1%d=0 then c(n1+1)(d+1)(r+1)else r
c n 1 0


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Edit: -2 characters from Oliver

• Welcome to PPCG! Does your program take stdin? You can use TIO, which has an online F# interpreter. Also, can remove the whitespace in r = if? Aug 16, 2017 at 17:41
• @Oliver Thank you, I changed the link to TIO, so now you can actually pass the argument to test it. :) Aug 21, 2017 at 6:52

Actually, 13 bytes

╗1⌠u;u@╜+%⌡╓u


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Explanation:

╗1⌠u;u@╜+%⌡╓u
╗              save n to register 0
1⌠u;u@╜+%⌡╓   first k (starting with k=0) where the following is truthy:
u             k+1
;u@╜+        n+k+1
%       (n+k+1)%(k+1)
u  increment


APL (Dyalog Unicode), 11 bytes

⊥⍨∘⌽0=⍳|-∘1


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Uses the alternative representation: the highest k such that 1..k divides n-1.

How it works

⊥⍨∘⌽0=⍳|-∘1  ⍝ Input: n
-∘1  ⍝ n minus 1
0=⍳|     ⍝ Is divisible by 1..n?
⊥⍨∘⌽         ⍝ Count the leading ones


"Count leading ones" idiom can be found on APLcart.

asm2bf, 74 bytes

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I/O format: In most cases, it's ASCII, yet some interpreters will output numbers in decimal representation. That's why the test case has 1 return 4 => because in fact, ASCII(1) is 49.

Golfed:

in r1
incr2
@l
movr3,r1
modr3,r2
ceqr3,0
cjn%l
decr2
outr2


Commented version:

; Read the number from the standard input.
in r1

; We start the division with 1.
inc r2

@l
; r3 = r1 mod r2
mov r3, r1
mod r3, r2

; if r3 is zero, then the streak
; isn't over.
ceq r3, 0

; Pass around next number and divisor.

; Loop
cjn %l

; Display the final result (it's always off-by-one), yet a dec fixes it.
dec r2
out r2


Brachylog, 10 bytes

∧.ℕ+↙?f-₁ⁿ


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 .            The output
∧             (which isn't necessarily the input)
ℕ           is a non-negative integer, and
f       the factors of
+↙?        it plus the input
-₁ⁿ    do not contain the output plus 1.


JavaScript (V8), 27 bytes

(n,i=2)=>n%i^1?--i:f(n,++i)


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Ruby, 39 bytes

->x{1.step{|i|break i-1if x%i!=0;x+=1}}


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R, 43 37 bytes

n=scan();which((n+1:n)%%(1:n+1)>0)[1]


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F#, 64 bytes

let d n=
let mutable m,l=n,1
while m%l=0 do m<-m+1;l<-l+1
l-1


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Simple explanation:

let divisibilityStreak n = // Arg: 'n'
let mutable l = 1         // For increase the 'divisible' number
let mutable n2 = n        // Another one for storing mutable 'n'
while n2 % l = 0 do       // While 'n' is divisible by 'l',
n2 <- n2 + 1             // Add 1 to both 'n2' (mutable 'n')...
l <- l + 1               // and 'l'
l - 1                     // Finally, return 'l - 1'


jq, 34 bytes

. as$x|0|until((.+$x)%(1+.)>0;.+1)


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jq, 40 bytes

[range(.)as$x|(.+$x)%(1+$x)<1//-$x]|-max


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TI-Basic, 19 21 bytes

Input N
Repeat remainder(N+Ans,Ans+1
Ans+1
End
Ans


Output is stored in Ans and displayed. This only works on TI-84+/SE with the 2.53 MP OS. The below version is 2 bytes bigger but works on earlier OS's.

21 23 bytes

Input N
Repeat fPart((N+Ans)/(Ans+1
Ans+1
End
Ans