OFFSET
1,1
COMMENTS
Are all terms odd? There are no even terms < 2*10^12.
MAPLE
select(n -> not isprime(n) and 2 &^n + 1 mod (numtheory:-sigma(n)-n) = 0, [$2..10^6]);
PROG
(PARI) is(n)=n>9 && !isprime(n) && Mod(2, sigma(n)-n)^n==-1 \\ Charles R Greathouse IV, Nov 18 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel and Altug Alkan, Nov 18 2016
STATUS
approved