OFFSET
1,1
EXAMPLE
Prime 13 is in sequence because sigma(2*13-1) = sigma(25) = 31 (prime).
PROG
(Magma) [p: p in PrimesUpTo(50000000) | IsPrime(SumOfDivisors(2*p-1))]
(PARI) forprime(p=1, 10^9, if(isprime(sigma(2*p-1)), print1(p, ", "))) \\ Derek Orr, Sep 25 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Sep 24 2014
STATUS
approved