A303737 - OEIS

%I #9 Jun 07 2018 04:26:41

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

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

%C a(9) > 10000. - _Giovanni Resta_, Jun 07 2018

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

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

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

%o (PARI) isok(k) = isprime((2*k)! + k! - 1); \\ _Michel Marcus_, May 28 2018

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

%K nonn,more

%O 1,2

%A _Muniru A Asiru_, May 27 2018

%E a(8) from _Giovanni Resta_, Jun 07 2018