OFFSET
1,2
COMMENTS
In hailstone sequences, only even powers of 2 are obtained as a final peak before descending to 1. [I assume this should really say: "These are numbers whose 3x+1 trajectory has the property that the final peak before descending to 1 is an even power of 2." - N. J. A. Sloane, Jul 22 2020]
REFERENCES
J. Heleen, Final Peak Sequences for Hailstone Numbers, 1993, preprint. [Apparently unpublished as of June 2017]
LINKS
FORMULA
EXAMPLE
The "3x+1" sequence starting at 21 is 21, 64, 32, 16, 8, 4, 2, 1, ..., and is the smallest start which contains 64 = 2^(2*3). So a(3) = 21. - N. J. A. Sloane, Jul 22 2020
PROG
CROSSREFS
KEYWORD
easy,nice,nonn
AUTHOR
Jeff Heleen, Apr 16 2000
STATUS
approved