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 A074472 #8 Oct 15 2013 22:31:30
%S A074472 1,8,20,112,23,97,34,77,76,44,136,135,134,133,145,206,130,191,141,96,
%T A074472 95,262,429,92,259,395,332,256,255,391,390,389,463,462,461,460,459,
%U A074472 458,457,456,455,454,502,501,451,499,498,753,496,495,494,749,492,747,490
%N A074472 Length of iteration sequence of Collatz-function (A006370) when initial value is 3^n (A000244) and final cycle is followed once.
%H A074472 T. D. Noe, <a href="/A074472/b074472.txt">Table of n, a(n) for n = 0..1000</a>
%e A074472 n=2: initial value=3^2, list of iterates is {9,28,14,7,22,11,34,17,52,26,13,50,20,10,5,16,8,4,2,1} length=a(2)=20; Observe that consecutive powers of 3 as arguments frequently provide iteration-lengths of consecutive integers, for instance n=10,11,12,13 give L=136,135,134,133 or n=88-96 result in L=1278-1271.
%t A074472 f[x_] := (1-Mod[x, 2])*(x/2)+(Mod[x, 2])*(3*x+1); f[1]=1; Table[1+Length[FixedPointList[f, 3^w]], {w, 1, 100}]
%Y A074472 Cf. A000244, A006370, A008884, A075484-A075488.
%K A074472 nonn
%O A074472 0,2
%A A074472 _Labos Elemer_, Sep 19 2002