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 A039503 #9 Dec 19 2015 12:57:10
%S A039503 1,3,11,15,29,39,43,53,57,59,65,69,71,77,79,85,87,95,97,101,103,105,
%T A039503 113,115,127,129,135,137,141,145,151,155,157,169,171,173,183,189,193,
%U A039503 201,205,207,211,217,227,231,235,245,249,253,259,269,273,275,283,289
%N A039503 Odd numbers from A039500.
%t A039503 colln[n_]:= NestWhile[If[EvenQ[#], #/2, 3#-1] &, n, FreeQ[{1, 5, 17}, #] &]; Select[Range[1, 289, 2], colln[#] == 1 &] (* _Jayanta Basu_, Jun 06 2013 *)
%Y A039503 Cf. A037084, A039500-A039505.
%K A039503 nonn,easy
%O A039503 1,2
%A A039503 _Christian G. Bower_, Feb 15 1999