A247789 Primes p such that sigma(2p-1) is a prime q.

5, 13, 1201, 1741, 2521, 5101, 8581, 14281, 41761, 139921, 353641, 595141, 697381, 1460341, 1639861, 3723721, 3889261, 6093541, 7956061, 11143921, 14199121, 33874681, 46938361, 51521401, 56063461, 62395621, 67523821, 90706981

Offset

1,1

Comments

Subsequence of A247820.

Corresponding values of primes q for a(n) are in A247836.

Links

Table of n, a(n) for n=1..28.

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

Cf. A000203, A008438, A000203, A247820.

Sequence in context: A157250 A009157 A153374 * A012032 A121228 A201260

Adjacent sequences: A247786 A247787 A247788 * A247790 A247791 A247792

Keyword

nonn

Author

Jaroslav Krizek, Sep 24 2014

Status

approved