OFFSET
1,2
COMMENTS
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).
LINKS
Michel Lagneau, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = A193688(n) - 2*n for n > 1.
EXAMPLE
a(8) = 31 because A193688(8)=47, and 47 - 2*8 = 31.
MATHEMATICA
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}]
Table[Length[NestWhileList[If[EvenQ[#], #/2, 3#+1]&, 3^n-1, #>1&]]-1, {n, 100}] (* Harvey P. Dale, Sep 06 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Mar 02 2013
STATUS
approved