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

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

Offset

1,2

Comments

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

Links

Table of n, a(n) for n=1..8.

Example

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.

Maple

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

Prog

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

Crossrefs

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

Sequence in context: A056147 A181857 A353162 * A180805 A120656 A256431

Adjacent sequences: A303734 A303735 A303736 * A303738 A303739 A303740

Keyword

nonn,more

Author

Muniru A Asiru, May 27 2018

Extensions

a(8) from Giovanni Resta, Jun 07 2018

Status

approved