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 A213214 Number of steps to reach 1 in the Collatz (3x+1) problem starting with 3^n - 1. 2
 1, 3, 10, 9, 96, 95, 32, 31, 43, 42, 134, 133, 132, 131, 99, 98, 190, 189, 139, 138, 261, 260, 427, 426, 394, 393, 330, 329, 390, 389, 388, 387, 461, 460, 459, 458, 457, 456, 455, 454, 453, 452, 500, 499, 498, 497, 496, 495, 494, 493, 492, 491, 746, 745, 488 (list; graph; refs; listen; history; text; internal format)
 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 Cf. A212653, A075487, A193688. Sequence in context: A202339 A234642 A038228 * A009030 A168331 A212354 Adjacent sequences: A213211 A213212 A213213 * A213215 A213216 A213217 KEYWORD nonn AUTHOR Michel Lagneau, Mar 02 2013 STATUS approved

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Last modified September 22 10:41 EDT 2023. Contains 365520 sequences. (Running on oeis4.)