OFFSET
1,2
EXAMPLE
240 doesn't qualify because 2^180-1 has 6291456 divisors but 2^240-1 has only 4718592 divisors.
CROSSREFS
KEYWORD
hard,nonn,more
AUTHOR
J. Lowell, May 11 2010
EXTENSIONS
Corrected and extended by Alois P. Heinz, Sep 13 2011
a(24)-a(30) from Amiram Eldar, Sep 02 2019
STATUS
approved