Quote:
Originally Posted by ATH
So perfectnumber+1 are prime for p=2,3,13 and 19 and unknown for p=132049 (79502 digits) which I trialfactored to 18*10^{9}.

Please note that if N=2^(p1)*(2^p1)+1 (where Mp=2^p1 is a Mersenne prime), then the primefactorization of N1 is known so a quick exact primetest is possible.