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 A044352 #11 Apr 18 2020 01:46:36
%S A044352 20,120,200,220,320,420,520,620,720,820,920,1020,1120,1200,1220,1320,
%T A044352 1420,1520,1620,1720,1820,1920,2000,2120,2200,2220,2320,2420,2520,
%U A044352 2620,2720,2820,2920,3020,3120,3200,3220,3320,3420
%N A044352 Numbers n such that string 2,0 occurs in the base 10 representation of n but not of n-1.
%C A044352 This is a (thin) subsequence of the terms of A121040 ending with a 2 followed by one or more zeros and which do not otherwise contain a 2 followed by a 0. This also demonstrates that this sequence is a 10-automatic. - _Charles R Greathouse IV_, Apr 18 2020
%H A044352 <a href="/index/Ar#10-automatic">Index entries for 10-automatic sequences</a>
%t A044352 SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{2,0}]>0,1,0],{n,3500}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Dec 24 2018 *)
%Y A044352 Subsequence of A121040.
%K A044352 nonn,base,easy
%O A044352 1,1
%A A044352 _Clark Kimberling_