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%I #13 Sep 06 2015 17:56:54
%S 1,3,10,9,96,95,32,31,43,42,134,133,132,131,99,98,190,189,139,138,261,
%T 260,427,426,394,393,330,329,390,389,388,387,461,460,459,458,457,456,
%U 455,454,453,452,500,499,498,497,496,495,494,493,492,491,746,745,488
%N Number of steps to reach 1 in the Collatz (3x+1) problem starting with 3^n - 1.
%C It is interesting to note that the quantity 3^n - 1 appears in the Collatz trajectory of 2^n - 1 after n iterations (see the formula).
%H Michel Lagneau, <a href="/A213214/b213214.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = A193688(n) - 2*n for n > 1.
%e a(8) = 31 because A193688(8)=47, and 47 - 2*8 = 31.
%t f[n_]:=Module[{a=3^n-1, k=0}, While[a>1, k++; If[EvenQ[a], a=a/2, a=a*3+1]]; k]; Table[f[n], {n,100}]
%t Table[Length[NestWhileList[If[EvenQ[#],#/2,3#+1]&,3^n-1,#>1&]]-1,{n,100}] (* _Harvey P. Dale_, Sep 06 2015 *)
%Y Cf. A212653, A075487, A193688.
%K nonn
%O 1,2
%A _Michel Lagneau_, Mar 02 2013
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