OFFSET
1,1
COMMENTS
a(7), if it exists, is at least 41519. - Charles R Greathouse IV, Jun 05 2013
2^41519 + 1 is the product of 3 and a composite number, so if a(7) exists, it exceeds 41519. - Jon E. Schoenfield, Feb 22 2022
EXAMPLE
11 is a term because 2^11 - 1 = 23*89 and 2^11 + 1 = 3*683.
PROG
(PARI) is(n)=isprime(n) && n>7 && ispseudoprime((2^n+1)/3) && bigomega(2^n-1)==2 \\ Charles R Greathouse IV, Jun 05 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Feb 27 2004
EXTENSIONS
a(6) from Robert G. Wilson v, Apr 18 2006
STATUS
approved