172
votes
Is this number a prime?
Hexagony, 29 bytes
.?'.).@@/'/.!.>+=(<.!)}($>(<%
The readable version of this code is:
...
- 3,401
138
votes
131
votes
67
votes
Coprimes up to N
Python 2, 61 47 bytes
lambda n:[k/n for k in range(n*n)if k/n*k%n==1]
Try it online!
Background
Consider the ring \$(Z_n, +_n, \cdot_n)\$. While this ring is ...
- 210k
53
votes
Is this number a prime?
Hexagony, 28 bytes
Since Etoplay absolutely trounced me on this question, I felt that I had to outgolf his only other answer.
...
- 11.6k
52
votes
Is this even or odd?
brainfuck, 8 bytes
+[,>,]<.
Input is in unary. Output is the 1 (truthy) for odd numbers and NUL (falsy) for even numbers.
Try it online!
How it works
We ...
- 210k
50
votes
Theoretically output Graham's number
Binary lambda calculus, 114 bits = 14.25 bytes
Hexdump:
00000000: 4457 42b0 2d88 1f9d 740e 5ed0 39ce 80 DWB.-...t.^.9..
Binary:
...
- 39.4k
49
votes
48
votes
Accepted
Is it a Proth number?
Jelly, 5 bytes
’&C²>
Try it online! or verify all test cases.
Let \$\newcommand{\&}[]{\text{ & }}j\$ be a strictly positive integer. \$j + 1\$ ...
- 210k
48
votes
Is it a Proth number?
Python, 22 bytes
lambda N:N-1&1-N>N**.5
This is a port of my Jelly answer. Test it on Ideone.
How it works
Let \$\newcommand{\&}[]{\text{ & }}j\$ ...
- 210k
46
votes
Calculate Phi (not Pi)
Regex (.NET), 122 113 bytes
^(?=((?=.*$(?<=^(\3+(.+.))(.*?(?>(.\4)?)))).)+(.*))((?=.*(?=\6$)(?<=(?!(.+.)\8*(?=\6$)(?<=^\8+))(.+?(?>\9?)))).)+
...
46
votes
44
votes
Accepted
Well that's odd... no wait, that's even!
CJam, 18 17 13 bytes
Thanks to aditsu for saving 4 bytes.
qW:O%eu~"eo"=
Try the test suite here. (The test suite is too long for the permalink. Just copy them ...
- 196k
41
votes
Theoretically output Graham's number
Haskell, 41 bytes
i=((!!).).iterate
i(($3).i(`i`1)(*3))4 64
Explanation:
(`i`1)f n = ...
- 39.4k
41
votes
Is this even or odd?
Mathematica, 4 bytes
OddQ
Gives True for odd inputs and False for even inputs, who knew?
...
- 196k
40
votes
40
votes
Accepted
Greatest Common Divisor
Retina, 16
^(.+)\1* \1+$
$1
This doesn't use Euclid's algorithm at all - instead it finds the GCD using regex matching groups.
Try it online. - This example ...
- 71.8k
37
votes
Accepted
Sharing (characters) is Caring!
20 languages
Using ()-#*.05;=>^Vefikloqrst (24 characters) so far:
...
- 68.1k
32
votes
Is this even or odd?
Taxi, 1,482 1,290 1,063 1,029 1,009 bytes
I've never written a program in Taxi before and I'm a novice in programming for general, so there are probably better ways to go about this. I've checked for ...
- 9,379
32
votes
Is this number evil?
JavaScript (ES6), 18 bytes
f=n=>n?!f(n&~-n):1
Try it online!
Explanation
The bitwise logic goes like this:
For integers, ...
- 188k
32
votes
Accepted
Make 1s using a bunch of 1s
score = 82 71 69 (34 ‘1’s + 23 ‘+’s + 12 parenthesis pairs)
$$\begin{multline*}
11111111111 = 1 + (1 + 1) \cdot {}
\\
(1 + 1 + 1 + (1 + 1)^{(1 + 1)^{1 + 1 + 1}}(1 + ((1 + 1)(1 + 1 + 1))^{1 + 1 + 1})) ...
- 39.4k
30
votes
Greatest Common Divisor
i386 (x86-32) machine code, 8 bytes (9B for unsigned)
+1B if we need to handle b = 0 on input.
amd64 (x86-64) machine code, 9 bytes (10B for unsigned, or 14B 13B ...
- 4,757
30
votes
Accepted
Longest Prime Sums
Score 100 8605
I used an algorithm that starts with one solution and repeatedly tries to split a prime \$p\$ in the solution into two other primes \$q_ 1\$ and \$q_ 2\$ that satisfy \$\frac1{p-1} = \...
- 15.4k
30
votes
Egyptian fraction representations of 1
Python 2, 42 bytes
f=lambda n,x=1:1/n*[x]or[x+1]+f(n-1,x*-~x)
Try it online!
The key thing to observe is that ...
- 22.3k
29
votes
29
votes
Accepted
How to solve the LCM in 50 bytes of Python
My solution to 50 bytes:
v=1
for x in input().split()*6**6:v+=-v%int(x)
print(v)
Explanation
The solution itself is relatively simple, but finding it was ...
- 22.3k
Only top scored, non community-wiki answers of a minimum length are eligible