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 A076291 #12 May 07 2022 09:26:43
%S A076291 2,1,3,2,1,3,2,4,2,1,5,1,3,8,1,3,2,1,9,2,1,5,1,3,12,2,1,3,2,4,2,1,17,
%T A076291 4,2,1,3,6,2,1,5,1,3,20,4,2,1,5,1,3,8,4,2,1,3,9,21,8,4,2,1,5,1,3,8,1,
%U A076291 3,2,1,9,2,1,5,1,3,36,8,4,2,1,9,2,1,5,1,3,9,3,8,4,2,1,5,1,3,14,1,3,9,29,16
%N A076291 a(n) = A002977(n+1) - A002977(n).
%H A076291 Amiram Eldar, <a href="/A076291/b076291.txt">Table of n, a(n) for n = 1..10000</a>
%H A076291 Benoit Cloitre, <a href="/A076291/a076291.jpg">Illustration of initial terms</a>
%t A076291 seq[max_] := Module[{s = Flatten[NestWhileList[Flatten[{2*# + 1, 3*# + 1}] &, 1, Min[#1] < max &]]}, Differences[Union[Select[s, # <= max &]]]]; seq[400000] (* _Amiram Eldar_, May 07 2022 *)
%Y A076291 Cf. A002977.
%K A076291 nonn
%O A076291 1,1
%A A076291 _Benoit Cloitre_, Nov 06 2002