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 A014887 #9 Oct 10 2021 16:33:18
%S A014887 1,3930,6044,61879,137256
%N A014887 n is equal to the number of 1's in all numbers <= n written in base 7.
%t A014887 Module[{nn=137300,dc},dc=Accumulate[DigitCount[Range[nn],7,1]];Position[ Thread[ {Range[nn],dc}],_?(#[[1]]==#[[2]]&),1,Heads-> False]]//Flatten (* _Harvey P. Dale_, Oct 10 2021 *)
%Y A014887 Cf. A014778, A014886.
%K A014887 nonn,base,fini,full
%O A014887 1,2
%A A014887 _Olivier Gérard_
%E A014887 List proved complete by _Hugo van der Sanden_ (cf. A014886).