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 A023798 #9 Jul 29 2021 17:33:29
%S A023798 0,1,2,3,5,6,7,11,15,19,21
%N A023798 Xenodromes: all digits in base 3 are different.
%t A023798 FromDigits[#,3]&/@Flatten[Permutations/@Subsets[{0,1,2}],1]//Union (* _Harvey P. Dale_, Jul 29 2021 *)
%K A023798 nonn,base,fini,full,easy
%O A023798 1,3
%A A023798 _Olivier Gérard_