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 A131613 #20 Sep 08 2022 08:45:31
%S A131613 0,1,3,4,5,7,8,11,12,16,19,20,21,29,32,56
%N A131613 Numbers k such that the decimal expansion of 3^k contains no 9.
%C A131613 I conjecture that 56 is the last term.
%t A131613 Join[{0}, Select[ Range@10000, FreeQ[ IntegerDigits[3^# ], 9] &]]
%o A131613 (Magma) [n: n in [0..1000] | not 9 in Intseq(3^n) ]; // _Vincenzo Librandi_, May 06 2015
%Y A131613 Numbers k such that the decimal expansion of 3^k contains no m: A030700 (m=0), A131627 (m=1), A131625 (m=2), A131629 (m=3), A131618 (m=4), A131617 (m=5), A131616 (m=6), A131615 (m=7), A131614 (m=8), this sequence (m=9).
%Y A131613 Cf. A007377.
%K A131613 base,fini,nonn
%O A131613 1,3
%A A131613 _Shyam Sunder Gupta_, Sep 01 2007
%E A131613 Adapted Mma and initial 0 added by _Vincenzo Librandi_, May 06 2015