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 A066904 #11 Jul 24 2021 23:25:21
%S A066904 1,3,6,15,15,10,10,21,21,21,6,105,105,28,28,28,28,28,15,15,15,15,15,
%T A066904 15,36,36,36,36,10,10,10,21,21,21,21,21,21,21,78,21,91,91,55,55,55,45,
%U A066904 45,45,45,45,45,45,45,45,120,120,120,120,120,120,120,120,66,66,136,136
%N A066904 Triangular numbers in A006577.
%H A066904 Harvey P. Dale, <a href="/A066904/b066904.txt">Table of n, a(n) for n = 0..2000</a>
%t A066904 Select[Table[Length[NestWhileList[If[EvenQ[#],#/2,3#+1]&,n,#!=1&]]-1, {n,1000}],OddQ[Sqrt[8#+1]]&] (* _Harvey P. Dale_, Feb 06 2015 *)
%Y A066904 Cf. A006577.
%K A066904 nonn
%O A066904 0,2
%A A066904 K. B. Subramaniam (kb_subramaniambalu(AT)yahoo.com), Dec 20 2001
%E A066904 More terms from _Sascha Kurz_, Mar 23 2002