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A127933 Number of halving and tripling steps to reach 1 from the n-th pure hailstone number in the '3x+1' problem. 2
0, 0, 7, 8, 16, 19, 9, 17, 20, 20, 7, 10, 23, 111, 18, 26, 21, 21, 34, 8, 29, 16, 11, 24, 112, 112, 32, 19, 107, 27, 14, 22, 115, 14, 35, 35, 22, 9, 30, 17, 17, 12, 118, 25, 25, 38, 113, 113, 69, 33, 33, 20, 20, 46, 108, 46, 121, 28, 28, 41, 15, 15, 23, 116, 116 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Previous name was: A006577(k), k = pure hailstone numbers from A061641.
Impure hailstone numbers are those which occur in the trajectories of smaller numbers. Thus 5 is impure since it occurs in the trajectory of 3.
LINKS
Douglas J. Shaw, The Pure Numbers Generated by the Collatz Sequence, The Fibonacci Quarterly, Vol. 44, Number 3, August 2006, p. 194.
FORMULA
a(n) = A006577(A061641(n)).
EXAMPLE
3 is the 3rd term of A061641, the trajectory of 3 has 7 terms: (10, 5, 16, 8, 4, 2, 1), so a(3) = 7.
CROSSREFS
Sequence in context: A125195 A099534 A318613 * A006878 A022312 A351087
KEYWORD
nonn
AUTHOR
Gary W. Adamson, Feb 08 2007
EXTENSIONS
Offset corrected and more terms added by Amiram Eldar, Feb 28 2020
Name edited by Michel Marcus, Feb 28 2020
STATUS
approved

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Last modified March 29 02:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)