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 A087721 #18 Dec 05 2022 08:35:28
%S A087721 2,3,4,5,6,8,10,11,12,16,20,21,22,23,24,25,30,32,38,39,40,41,42,43,44,
%T A087721 45,46,47,48,52,54,56,58,60,61,62,64,66,68,71,72,73,77,78,79,80,82,83,
%U A087721 85,87,88,90,91,92,93,94,96,101,106,108,109,111,114,115,118,120,122,123
%N A087721 Strictly increasing domain of A005185.
%t A087721 digits=750;
%t A087721 Hofstadter[n_Integer?Positive] := Hofstadter[n] = Hofstadter[n - Hofstadter[n-1]] + Hofstadter[n - Hofstadter[n-2]];
%t A087721 Hofstadter[1] = Hofstadter[2] = 1;
%t A087721 a1=Table[Hofstadter[n], {n, digits}];
%t A087721 f[x_, y_] := x-y/; x-y>0;
%t A087721 f[x_, y_] := 0/; x-y<=0;
%t A087721 b=Table[If[f[a1[[n]], a1[[n-1]]]>0, a1[[n]], 0], {n, 2, digits}];
%t A087721 c=Delete[Union[b], 1]
%Y A087721 Cf. A005185, A087722, A087723.
%K A087721 nonn
%O A087721 1,1
%A A087721 _Roger L. Bagula_, Sep 29 2003