

A057652


Numbers n such that n2^k is a lucky number for all k such that 1 < 2^k < n.


1




OFFSET

1,2


COMMENTS

Perhaps there are no more terms?
Lucky numbers have asymptotic properties very similar to prime numbers, so one can conjecture finiteness of this sequence in the same way as ErdÅ‘s did for A039669, and this should generalize to any sequence created using a similar sieve.  M. F. Hasler, Oct 15 2010


LINKS

Table of n, a(n) for n=1..7.


EXAMPLE

647 is in this sequence since 6472, 6474, 6478, 64716, 64732, 64764, 647128, 647256, 647512 are all members of the sequence A000959 of lucky numbers.  M. F. Hasler, Oct 15 2010


PROG

(PARI) A057652(Nmax) = { my(v=vector(Nmax\2, i, 2*i1)); for(i=2, #v, v[i]>#v & break; v=vecextract(v, 2^#v1sum(k=1, #v\v[i], 2^(v[i]*k))>>1)); v=Set(v); for(n=1, Nmax, for(k=1, Nmax, 2^k<n  break; setsearch(v, n2^k)  next(2)); print1(n", ")) } /* M. F. Hasler, Oct 15 2010 */


CROSSREFS

Cf. A000959, A039669.
Sequence in context: A097048 A244914 A227126 * A025067 A024371 A231479
Adjacent sequences: A057649 A057650 A057651 * A057653 A057654 A057655


KEYWORD

nonn,hard,more


AUTHOR

Naohiro Nomoto, Oct 14 2000


EXTENSIONS

Added initial terms {1, 2}, reworded definition following a suggestion from D. Forgues.  M. F. Hasler, Oct 15 2010


STATUS

approved



