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

Author

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

Keywords

• nonn

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.

Examples

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

Links

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

Crossrefs

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

Programs

Maple

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

PARI

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