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 A199636 #10 Mar 30 2012 17:23:03
%S A199636 5,3,21,13,85,17,53,11,35,113,341,7,23,69,75,213,227,15,45,141,151,
%T A199636 453,1365,9,29,93,277,301,853,909,19,61,181,201,565,605,1813,5461,37,
%U A199636 117,369,373,401,403,1109,1137,1205,3413,3637,25,77,81,241,245,267,725
%N A199636 Irregular rows of odd numbers that produce n even numbers in their Collatz iteration.
%C A199636 It is conjectured that every odd number greater than 1 eventually appears in this sequence. The smallest and largest terms in row n are A199637(n) and A199638(n). The number of terms in row n is A131450(n) for n > 3.
%C A199636 The 10th and 20th rows are A199817 and A199818.
%H A199636 T. D. Noe, <a href="/A199636/b199636.txt">Rows n = 4..33, flattened</a>
%t A199636 Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; nn = 16; t = Table[{}, {nn}]; Do[len = Length[Select[Collatz[n], EvenQ]]; If[0 < len <= nn, AppendTo[t[[len]], n]], {n, 1, 25000, 2}]; t
%K A199636 nonn,tabf
%O A199636 4,1
%A A199636 _T. D. Noe_, Nov 14 2011