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 A250069 #22 Feb 25 2018 12:43:15
%S A250069 1,4,4,16,12,36,4,12,40,100,60,28,16,196,112,256,28,12,180,400,16,96,
%T A250069 52,576,312,676,72,156,420,52,36,40,108,88,612,1296,136,16,760,1600,
%U A250069 28,352,36,148,1012,72,16,460,1200,60,1300,540,280,2916,88,3136,12
%N A250069 a(n) = n^2 mod gpf(n^2 + 1) where gpf(k) is the greatest prime dividing k.
%C A250069 For n > 1, a(n) == 0 (mod 4).
%H A250069 Michel Lagneau, <a href="/A250069/b250069.txt">Table of n, a(n) for n = 1..10000</a>
%F A250069 a(n) = n^2 mod A014442(n) where A014442(n) is the greatest prime factor of n^2 + 1.
%e A250069 a(5)=12 because 5^2 mod A014442(5) = 25 mod 13 = 12.
%p A250069 with(numtheory):
%p A250069 for n from 1 to 500 do:
%p A250069 p:=n^2+1:x:=factorset(p):n0:=nops(x):r:=irem(n^2,x[n0]):
%p A250069 printf(`%d, `, r):
%p A250069 od:
%t A250069 Table[Mod[n^2,FactorInteger[n^2+1,FactorComplete->True][[-1,1]]],{n,100}]
%o A250069 (PARI) a(n) = lift(Mod(n, vecmax(factor(n^2+1)[,1]))^2); \\ _Michel Marcus_, Sep 13 2017
%Y A250069 Cf. A006530, A014442.
%K A250069 nonn,easy
%O A250069 1,2
%A A250069 _Michel Lagneau_, Nov 11 2014
%E A250069 Edited: exchanged name with an old comment. Old name as an alternative formula. Keyword easy added. - _Wolfdieter Lang_, Nov 29 2014
%E A250069 Redundancy in Name and in Formula section removed (at the suggestion of _Michel Marcus_) by _Jon E. Schoenfield_, Sep 13 2017