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 A258189 #57 Jul 25 2021 02:39:58
%S A258189 10101,11111,101121,220212,222001,1022011,1111221,2010002,2101001,
%T A258189 2121001,10101022,10122201,10201001,10212111,11111112,11121201,
%U A258189 12010221,20210202,21121121,100001111,101010101,102112011,110020001,112112001,120002211,122000101,201201201,202212002
%N A258189 Pseudoprimes to base 3, written in base 3.
%H A258189 Amiram Eldar, <a href="/A258189/b258189.txt">Table of n, a(n) for n = 1..10000</a>
%F A258189 a(n) = A007089(A005935(n)). - _Michel Marcus_, Sep 11 2015
%t A258189 base = 3; t = {}; n = 1;
%t A258189 While[Length[t] < 40, n++;
%t A258189 If[! PrimeQ[n] && PowerMod[base, n - 1, n] == 1,
%t A258189 AppendTo[t, FromDigits@IntegerDigits[n, 3]]]]; t
%o A258189 (PARI) lista(nn, b=3) = {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 A258189 Cf. A005935 (pseudoprimes to base 3), A007089 (numbers in base 3).
%Y A258189 Cf. A262101, A262102, A262103, A262104, A262105, A262154.
%K A258189 nonn,base
%O A258189 1,1
%A A258189 _Abdul Gaffar Khan_, Sep 11 2015
%E A258189 a(25) corrected by _Georg Fischer_, Dec 18 2020