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 A135590 #21 Nov 05 2023 09:04:13
%S A135590 216,948,1560,4872,8208,9828,18200,29640,37024,65536,89550,283800,
%T A135590 535920,592956,649800,825930,1042320,1382400,1536220,3688230,4215120,
%U A135590 4321800,5103210,19078930,21415680,24471720,214067490,435457620,535019100
%N A135590 Numbers k such that k^2 + 1 is a Sarrus number (pseudoprime to base 2).
%C A135590 Note that A000215(5) corresponds to a(10), and A000215(6) corresponds to a(33), and in general when A000215(n) is composite, this sequence has corresponding entry. - _Jeppe Stig Nielsen_, Mar 26 2016
%H A135590 Amiram Eldar, <a href="/A135590/b135590.txt">Table of n, a(n) for n = 1..40</a> (terms 1..33 from Jeppe Stig Nielsen)
%t A135590 fQ[n_] := ( !PrimeQ[n^2 + 1] && PowerMod[2, n^2, n^2 + 1] == 1); lst = {}; Do[ If[ fQ@ n, AppendTo[lst, n]], {n, 2, 440000000, 2}]; lst (* _Robert G. Wilson v_, Apr 18 2008 *)
%o A135590 (PARI) is(n) = {Mod(2, n)^(n-1)==1 && !ispseudoprime(n) && n > 1};
%o A135590 for(n=1, 1e10, if(is(n^2+1), print1(n, ", "))); \\ _Altug Alkan_, Mar 26 2016
%Y A135590 Cf. A000215, A001567, A002522, A005574.
%K A135590 nonn
%O A135590 1,1
%A A135590 _Jason Earls_, Feb 25 2008
%E A135590 More terms from _Robert G. Wilson v_, Apr 18 2008