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%I #8 Oct 15 2013 22:31:31
%S 8,6,20,13,27,28,122,123,36,37,157,114,53,54,99,100,101,102,103,73,
%T 167,168,169,170,171,172,248,174,188,189,252,253,179,180,318,244,196,
%U 197,154,155,156,157,401,327,496,497,162,163,332,333,409,472,411,412,338
%N Length of iteration list when Collatz-function is iterated with initial value 2^n + 1.
%C n=4, 1+2^n = 17, list = {17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1}, so a(4) = 13.
%H T. D. Noe, <a href="/A075486/b075486.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = A008908(2^n+1).
%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, A075487-A075488.
%K nonn
%O 1,1
%A _Labos Elemer_, Sep 26 2002
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