A339862 Primes p such that p + sigma(p-1) is prime.

2, 7, 11, 13, 23, 31, 41, 43, 53, 59, 61, 67, 89, 97, 107, 109, 127, 131, 151, 167, 179, 181, 193, 211, 227, 233, 251, 263, 271, 283, 293, 307, 311, 313, 317, 353, 397, 409, 431, 439, 457, 487, 503, 523, 541, 563, 571, 599, 607, 613, 619, 631, 653, 659, 661, 673, 701, 709, 739, 743, 773, 787, 809

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

a(3)=11 is a term because 11 is prime, sigma(11-1)=1+2+5+10=18, and 11+18=29 is prime.

Maple

select(t -> isprime(t) and isprime(t+numtheory:-sigma(t-1)), [2, seq(i, i=3..1000, 2)]);

Mathematica

Select[Prime[Range[200]], PrimeQ[#+DivisorSigma[1, #-1]]&] (* Harvey P. Dale, Sep 08 2024 *)

Crossrefs

Cf. A000203.

Sequence in context: A019346 A045369 A157975 * A045370 A117048 A040128

Adjacent sequences: A339859 A339860 A339861 * A339863 A339864 A339865

Keyword

nonn

Author

J. M. Bergot and Robert Israel, Dec 19 2020

Status

approved