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 A020169 #19 Sep 08 2022 08:44:45
%S A020169 4,8,10,15,20,21,35,40,105,145,231,344,561,609,645,671,703,841,1065,
%T A020169 1105,1281,1387,1417,1729,1885,1891,2121,2465,2701,2821,3045,3053,
%U A020169 3829,4033,4205,4521,4870,5365,5565,6161,6892,7957,8295,8321,8695,8905,8911,9253
%N A020169 Pseudoprimes to base 41.
%C A020169 Composite numbers n such that 41^(n-1) == 1 (mod n).
%H A020169 R. J. Mathar, <a href="/A020169/b020169.txt">Table of n, a(n) for n=1..1003</a>
%H A020169 <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>
%t A020169 base = 41; t = {}; n = 1; While[Length[t] < 100, n++; If[! PrimeQ[n] && PowerMod[base, n-1, n] == 1, AppendTo[t, n]]]; t (* _T. D. Noe_, Feb 21 2012 *)
%o A020169 (Magma) [n: n in [1..3*10^4] | IsOne(Modexp(41, n-1, n)) and not IsPrime(n)]; // _Vincenzo Librandi_, Mar 15 2019
%Y A020169 Cf. A001567 (pseudoprimes to base 2).
%K A020169 nonn
%O A020169 1,1
%A A020169 _David W. Wilson_