A303737 Numbers k such that (2*k)! + k! - 1 is prime.

1, 4, 18, 49, 60, 82, 321, 6328

Offset: 1

Author

Muniru A Asiru, May 27 2018

Keywords

• nonn
• more

Comments

a(9) > 10000. - Giovanni Resta, Jun 07 2018

Examples

			1 is a term because (2*1)! + 1! - 1 = 2 which is a prime.
4 is a term because (2*4)! + 4! - 1 = 40343 which is a prime.
		

Crossrefs

Cf. A242487, A300947, A303738 (corresponding primes).

Programs

Maple

select(k->isprime(factorial(2*k)+factorial(k)-1),[$1..1000]);

PARI

isok(k) = isprime((2*k)! + k! - 1); \\ Michel Marcus, May 28 2018

Extensions

a(8) from Giovanni Resta, Jun 07 2018