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 A031903 #12 Nov 16 2019 03:28:31
%S A031903 957,1797,2943,3003,3027,3153,3747,4227,4695,4761,5211,5547,5637,6621,
%T A031903 7629,7737,8253,8535,9915,9957,10173,10311,10341,11157,12357,12519,
%U A031903 12699,13677,13893,14775,14817,14997,15291,15333,15417,15567
%N A031903 Lucky numbers with size of gaps equal to 20 (upper terms).
%H A031903 Amiram Eldar, <a href="/A031903/b031903.txt">Table of n, a(n) for n = 1..10000</a>
%t A031903 t = Range[1, 20000, 2]; sieve[n_] := Module[{k = t[[n]]}, t = Delete[t, Table[{i}, {i, k, Length[t], k}]]]; n = 1; While[ t[[n]] < Length[t], n++; sieve[n]]; Transpose[Select[Partition[t,2,1], Last[#]- First[#]==20&]][[2]] (* _Harvey P. Dale_, Apr 07 2011 *)
%Y A031903 Cf. A000959, A031902.
%K A031903 nonn
%O A031903 1,1
%A A031903 _Patrick De Geest_