A247836 Primes p of the form sigma(2q-1) where q is a prime.

13, 31, 2801, 3541, 5113, 10303, 17293, 30941, 88741, 292561, 732541, 1191373, 1395943, 2922391, 3281533, 7450171, 7781311, 12190573, 15916111, 22292563, 28792661, 67757593, 93886411, 103052953, 112137511, 124802413, 135059263, 181427431

Offset: 1

Author

Jaroslav Krizek, Sep 24 2014

Keywords

• nonn

Comments

Subsequence of A247837.

Examples

			Prime 13 is in sequence because there is prime 5 such that sigma(2*5-1) = sigma(9) = 13.
		

Crossrefs

Cf. A000203, A247837, A247820.

Programs

Magma

Sort([a: p in PrimesUpTo(5000000) | IsPrime(a) where a is SumOfDivisors(2*p-1)]); // corrected by Jaroslav Krizek, Nov 16 2014

Mathematica

Select[DivisorSigma[1,2Prime[Range[3*10^6]]-1],PrimeQ] (* The program generates the first 23 terms of the sequence. *) (* Harvey P. Dale, Jul 17 2025 *)

PARI

forprime(p=1,10^9,if(isprime(sigma(2*p-1)),print1(sigma(2*p-1),", "))) \\ Derek Orr, Sep 25 2014