A247955 - OEIS

A247955

Primes p such that there is prime q with sigma(q+2) = p.

7, 13, 31, 1093, 2801, 5113, 8011, 17293, 30103, 30941, 86143, 459007, 552793, 579883, 732541, 1191373, 3500201, 3730693, 4534771, 5168803, 5333791, 7450171, 10378063, 25646167, 25882657, 28792661, 30266503, 43553401, 48037081, 52265671, 56964757, 62433703, 65504743, 67856407, 76413823, 77572057

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Primes p such that there is prime q such that A000203(q+2) = p.

Primes p of the form sigma(A171130(n)) in increasing order.

LINKS

Table of n, a(n) for n=1..36.

MATHEMATICA

Sort[Select[DivisorSigma[1, #+2]&/@Prime[Range[5200000]], PrimeQ]] (* Harvey P. Dale, Apr 27 2022 *)

PROG

(PARI) v=[]; forprime(p=1, 10^8, if(ispseudoprime(sigma(p+2)), v=concat(v, sigma(p+2)))); v \\ Derek Orr, Oct 26 2014