A062056 Numbers with 6 odd integers in their Collatz (or 3x+1) trajectory.

7, 14, 15, 28, 29, 30, 56, 58, 60, 61, 112, 116, 117, 120, 122, 224, 232, 234, 240, 241, 244, 245, 267, 448, 464, 468, 469, 480, 482, 483, 488, 490, 497, 534, 535, 537, 896, 928, 936, 938, 960, 964, 965, 966, 976, 980, 981, 985, 994, 995, 1068, 1069, 1070, 1073

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Comments

The Collatz (or 3x+1) function is f(x) = x/2 if x is even, 3x+1 if x is odd.

The Collatz trajectory of n is obtained by applying f repeatedly to n until 1 is reached.

A078719(a(n)) = 6; A006667(a(n)) = 5.

Examples

			The Collatz trajectory of 7 is (7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1), which contains 6 odd integers.
		

References

• J. Shallit and D. Wilson, The "3x+1" Problem and Finite Automata, Bulletin of the EATCS #46 (1992) pp. 182-185.

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
• J. Shallit and D. Wilson, The "3x+1" Problem and Finite Automata, Bulletin of the EATCS #46 (1992) pp. 182-185.
• Eric Weisstein's World of Mathematics, Collatz Problem
• Wikipedia, Collatz conjecture
• Index entries for sequences related to 3x+1 (or Collatz) problem
• Index entries for 2-automatic sequences.

Crossrefs

Cf. A062052-A062060.

Column k=6 of A354236.

Programs

Haskell

import Data.List (elemIndices)
a062056 n = a062056_list !! (n-1)
a062056_list = map (+ 1) $ elemIndices 6 a078719_list
-- Reinhard Zumkeller, Oct 08 2011

Mathematica

Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; countOdd[lst_] := Length[Select[lst, OddQ]]; Select[Range[1000], countOdd[Collatz[#]] == 6 &] (* T. D. Noe, Dec 03 2012 *)