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 A262101 #35 Jul 25 2021 02:40:04
%S A262101 33,1111,1123,11111,12303,13003,20301,22011,22333,101101,103133,
%T A262101 103313,111223,120231,122133,123001,131203,131301,133333,200113,
%U A262101 212201,222031,230011,300331,303031,310213,321203,333001,1010101,1010103,1021021,1022323,1023323,1111111,1112233,1213021,1213303,1330111,2002001,2010201,2013313,2023033,2031211,2032223
%N A262101 Pseudoprimes to base 4, written in base 4.
%H A262101 Amiram Eldar, <a href="/A262101/b262101.txt">Table of n, a(n) for n = 1..10000</a>
%F A262101 a(n) = A007090(A020136(n)).
%t A262101 BaseForm[Select[Range[4096], Not[PrimeQ[#]] && PowerMod[4, # - 1, #] == 1 &], 4]
%o A262101 (PARI) lista(nn, b=4) = {for (n=1, nn, if (Mod(b, n)^(n-1)==1 && !ispseudoprime(n) && n>1, print1(subst(Pol(digits(n,b), x), x, 10), ", ");););} \\ _Michel Marcus_, Sep 30 2015
%Y A262101 Cf. A007090 (numbers in base 4), A020136 (pseudoprimes to base 4).
%Y A262101 Cf. A258189, A262102, A262103, A262104, A262105, A262154.
%K A262101 nonn,base
%O A262101 1,1
%A A262101 _Abdul Gaffar Khan_, Sep 11 2015