A308169 Numbers k such that A023896(k) mod A000203(k) is prime.

3, 7, 10, 11, 16, 19, 22, 23, 25, 27, 31, 34, 43, 46, 49, 58, 59, 71, 79, 82, 83, 94, 100, 103, 106, 118, 121, 131, 139, 142, 163, 166, 178, 191, 199, 202, 208, 211, 214, 223, 226, 251, 262, 271, 274, 298, 311, 331, 334, 346, 358, 359, 379, 382, 383, 394, 419, 443, 454, 463, 466, 478, 479, 484

Offset

1,1

Comments

Numbers k such that (k*A000010(k)/2) mod A000203(k) is prime.

The primes in the sequence are A092109.

The even semiprimes in the sequence are A112774.

Links

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

Example

a(3)=10 is in the sequence because A023896(10) mod A000203(10) = 20 mod 6 = 2, and 2 is prime.

Maple

select(n -> isprime((n*numtheory:-phi(n)/2) mod numtheory:-sigma(n)), [$2..1000]);

Prog

(PARI) isok(n) = isprime(n*eulerphi(n)/2 % sigma(n)); \\ Michel Marcus, May 15 2019

Crossrefs

Cf. A000010, A000203, A023896, A092109, A112774.

Sequence in context: A213687 A226934 A238506 * A343225 A363245 A276117

Adjacent sequences: A308166 A308167 A308168 * A308170 A308171 A308172

Keyword

nonn

Author

J. M. Bergot and Robert Israel, May 15 2019

Status

approved