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 A248219 #17 Mar 22 2017 03:39:25
%S A248219 1,3,7,19,21,31,37,43,57,93,111,129,133,157,217,259,301,307,313,399,
%T A248219 463,471,499,589,613,651,703,777,817,903,921,939,967,1099,1147,1333,
%U A248219 1389,1497,1591,1767,1839,2109,2149,2191,2451,2683,2901,2983,3241,3297,3441
%N A248219 Indices where A248218(n) = 1.
%C A248219 n is in the sequence if there exists a number k0 such that A003095(k) mod n = A003095(k0) mod n for all k >= k0.
%C A248219 Conjecture: a(n) ~ n^2.
%H A248219 Vaclav Kotesovec, <a href="/A248219/b248219.txt">Table of n, a(n) for n = 1..717</a>
%e A248219 7 is in the sequence since A003095 mod 7 is {1, 2, 5, 5, 5, 5, ...}, k0 = 3, A003095(k) mod 7 = 5 for all k >= k0. The period is 1.
%e A248219 10 is not in the sequence since A003095 mod 10 is {1, 2, 5, 6, 7, 0, 1, 2, 5, 6, 7, 0, 1, 2, ...} and the period is 6, not 1.
%t A248219 nmax=10000; periods=Table[m=Rest[NestList[Mod[#^2+1,n]&,0,nmax]]; period=0; j=1; While[j<=Length[m]&&period==0,If[m[[Length[m]-j]]==m[[Length[m]]],period=j]; j++]; period,{n,1,nmax}]; Select[Range[nmax],periods[[#]]==1&]
%Y A248219 Cf. A003095, A247981, A248218.
%K A248219 nonn
%O A248219 1,2
%A A248219 _Vaclav Kotesovec_, Oct 04 2014