OFFSET
1,1
COMMENTS
A candidate for the next term is a(32) = 634. 2^634-635 is composite with 191 decimal digits and unknown factorization. - Hugo Pfoertner, Aug 13 2007
LINKS
EXAMPLE
a(3) = 6 because 2^6-6-1 = 57 = 3*19 is a semiprime.
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Hugo Pfoertner, Oct 18 2004
EXTENSIONS
More terms from Hugo Pfoertner, Aug 13 2007
a(24) corrected by Hugo Pfoertner, Sep 07 2017
STATUS
approved