A076683 Numbers k such that 7*k! + 1 is prime.

3, 7, 8, 15, 19, 29, 36, 43, 51, 158, 160, 203, 432, 909, 1235, 3209, 8715, 9707

Offset: 1

Author

Phillip L. Poplin (plpoplin(AT)bellsouth.net), Oct 25 2002

Keywords

• nonn
• more

Comments

a(17) > 5830. - Jinyuan Wang, Feb 05 2020

a(19) > 12000. - Michael S. Branicky, Jul 04 2024

Examples

			k = 3 is here because 7*3! + 1 = 43 is prime.
		

Crossrefs

Cf. A002981, A051915, A076679, A076680, A076681, A076682, A178488, A180626, A126896.

Programs

PARI

is(k) = ispseudoprime(7*k!+1); \\ Jinyuan Wang, Feb 05 2020

Python

from sympy import isprime
from math import factorial
def aupto(m): return [k for k in range(m+1) if isprime(7*factorial(k)+1)]
print(aupto(300)) # Michael S. Branicky, Mar 07 2021

Extensions

a(17)-a(18) from Michael S. Branicky, Jul 04 2024