This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A235363 #7 Feb 16 2025 08:33:21
%S A235363 0,0,0,0,7,0,0,11,0,0,15,0,21,19,0,0,23,1,0,27,0,0,22,0,43,35,0,1,39,
%T A235363 0,0,43,53,0,47,0,0,51,1,0,55,0,69,59,0,79,63,1,0,67,0,0,50,0,0,75,0,
%U A235363 1,79,1,111,83,101,0,87,0,115,91,0,0,95,1,117,99,0,0,103,1,0,107,1,0,78,0,157,115,0,151,119,0,0,123,149,1,127,0,0,131,0,0,135
%N A235363 (1 + Sum_{k=1..m-1} k^(m-1)) (mod m), for m = 1, 3, 5, 7, 9, ...
%C A235363 a(n) = (1 + Sum_{k=1..2*n} k^(2*n)) (mod 2*n+1), for n = 0, 1, 2, 3, ...
%C A235363 The Agoh-Giuga Conjecture is that a(n)=0 iff 2*n+1 is 1 or a prime.
%H A235363 MathWorld, <a href="https://mathworld.wolfram.com/GiugasConjecture.html">Giuga's Conjecture</a>
%H A235363 Wikipedia, <a href="http://en.wikipedia.org/wiki/Agoh-Giuga_conjecture">Agoh-Giuga conjecture</a>
%F A235363 a(n) = 0 iff A235364(n) = 0.
%t A235363 Table[ Mod[ Sum[ PowerMod[ k, n - 1, n], {k, n - 1}] + 1, n], {n, 1, 201, 2}]
%Y A235363 Cf. A007850, A046094, A204187, A228037, A235364.
%K A235363 nonn
%O A235363 0,5
%A A235363 _Jonathan Sondow_, Jan 07 2014