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 A031008 #13 Apr 10 2020 07:45:42
%S A031008 0,7,21,35,49,63,77,91,92,95,98,101,104,107,110,112,133,154,175,196,
%T A031008 217,238,239,242,245,248,251,254,257,259,280,301,322,343,364,385,386,
%U A031008 389,392,395,398,401,404,406,427,448,469,490,511
%N A031008 Position of n-th 0 in A031007.
%t A031008 Rest[Flatten[Position[Flatten[Table[Reverse[IntegerDigits[n,7]],{n,0,200}]],0]]]-1 (* _Harvey P. Dale_, Jun 08 2017 *)
%K A031008 nonn,base
%O A031008 1,2
%A A031008 _Clark Kimberling_
%E A031008 Missing a(1)=0 inserted by _Sean A. Irvine_, Apr 10 2020