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 A185589 #18 Mar 01 2019 09:00:56
%S A185589 144,96,64,85,113,151,201,134,179,239,319,425,567,378,252,168,112,149,
%T A185589 199,265,353,471,314,419,559,745,993,662,883,1177,1569,1046,1395,930,
%U A185589 620,827,1103,1471,1961,2615,3487,4649,6199,8265,5510,7347,4898,6531,4354,5805,3870,2580,1720,2293,3057,2038,2717,3623,4831
%N A185589 Iterate the map in A006369 starting at 144.
%C A185589 Lagarias, page 270, appears to imply that this trajectory has period 12 and smallest element 144, which is not true.
%D A185589 J. C. Lagarias, ed., The Ultimate Challenge: The 3x+1 Problem, Amer. Math. Soc., 2010; see page 270.
%H A185589 Reinhard Zumkeller, <a href="/A185589/b185589.txt">Table of n, a(n) for n = 1..10000</a>
%H A185589 <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a>
%t A185589 f[n_] := If[Mod[n, 3] == 0, 2*n/3, Round[4*n/3]]; a[1] = 144; a[n_] := a[n] = f[a[n - 1]]; Table[a[n], {n, 1, 59}] (* _Jean-François Alcover_, Jun 10 2013 *)
%t A185589 SubstitutionSystem[{n_ :> Switch[Mod[n, 3], 0, 2n/3, 1, (4n - 1)/3, _, (4n + 1)/3]}, {144}, 60] // Flatten (* _Jean-François Alcover_, Mar 01 2019 *)
%o A185589 (Haskell)
%o A185589 a185589 n = a185589_list !! (n-1)
%o A185589 a185589_list = iterate a006369 144 -- _Reinhard Zumkeller_, Dec 31 2011
%Y A185589 Cf. A028394, A028396, A094328, A094329, A185590.
%K A185589 nonn
%O A185589 1,1
%A A185589 _N. J. A. Sloane_, Feb 04 2011