

A127789


Record indices of 2^h(n)/(3^t(n)*n), where h and t are the number of halving resp. tripling steps in the '3x + 1' problem.


6




OFFSET

1,2


COMMENTS

Original name: In the '3x + 1' problem we would expect a positive integer n to be approximately equal to 2^j / 3^k where j is the number of halving steps and k is the number of '3x + 1' steps required to reach 1. The numbers in this sequence are those for which 2^j / (n*3^k) sets a new record.
Eric Roosendaal calls 2^j / (n*3^k) the residue of n and conjectures that 993 yields the highest residue.  T. D. Noe, Apr 08 2007
It has been verified that the next value, if it exists, is larger than 2^32 ~ 4.3e9. We do not need an "escape clause" (as for A006577, A006666, A006667, ...) in this sequence since the unlikely case of a possibly undefined ratio is irrelevant for the list of records.  M. F. Hasler, May 07 2018


LINKS

Table of n, a(n) for n=1..8.
Eric Roosendaal, On the 3x+1 Problem


PROG

(PARI) (c(n, c=[0, 0])=while(n>1, bittest(n, 0)&&c[1]++&&(n=n*3+1)&&next; n\=2; c[2]++); c); m=1; for(n=1, oo, m<<(t=c(n))[2]>n*3^t[1]next; m=n*3^t[1]/2^t[2]; print1(n", ")) \\ M. F. Hasler, May 07 2018


CROSSREFS

Cf. A006370 (Collatz map), A014682 (condensed version using (3n+1)/2).
Cf. A006666 (halving steps), A006667 (tripling steps), A006577 (total).
Sequence in context: A152607 A118559 A189244 * A112105 A065501 A144385
Adjacent sequences: A127786 A127787 A127788 * A127790 A127791 A127792


KEYWORD

more,nonn


AUTHOR

Paul Boddington, Apr 04 2007


EXTENSIONS

New name from M. F. Hasler, May 07 2018


STATUS

approved



