OFFSET
1,1
COMMENTS
There are no others up to 1.6*10^13, but there are at least 20 larger ones, between 87916260096000 and 19424258892617980729341453189120.
Ligh & Wall found a(1), a(4) and a(5). - Amiram Eldar, Sep 27 2018
LINKS
Steve Ligh and Charles R. Wall, Functions of Nonunitary Divisors, Fibonacci Quarterly, Vol. 25 (1987), pp. 333-338.
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Dean Hickerson, Sep 25 2001
STATUS
approved