%I #12 Dec 15 2023 08:01:04

%S 1,8,17,18,107,108,47,48,62,63,157,158,159,160,130,131,225,226,178,

%T 179,304,305,474,475,445,446,385,386,449,450,451,452,528,529,530,531,

%U 532,533,534,535,536,537,587,588,589,590,591,592,593,594,595,596,853,854

%N Length of iteration list when Collatz-function is iterated with initial value 2^n - 1.

%C Somewhat surprisingly, these iterations take almost twice as long as the iterations for 2^n + 1. See A075486. - _T. D. Noe_, Jan 17 2013

%H T. D. Noe, <a href="/A075485/b075485.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a>

%F a(n) = A008908(2^n-1).

%e n=4, 2^n - 1 = 15, list = {15, 46, 23, 70, 35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1}, so a(4) = 18.

%t Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; Table[Length[Collatz[2^n - 1]], {n, 100}] (* _T. D. Noe_, Jan 17 2013 *)

%Y Cf. A006370, A008908, A074472, A075484, A075486, A075487, A075488.

%K nonn

%O 1,2

%A _Labos Elemer_, Sep 26 2002