A116896 Numbers k such that k! + k!! + 1 is prime, where k!! denotes double factorial (A006882).

0, 1, 2, 6, 42, 604, 1976, 5126, 14124

Offset: 1

Author

Giovanni Resta, Mar 04 2006

Keywords

• hard
• more
• nonn

Comments

1976! + 1976!! + 1 is a 5657-digit prime. Next term is greater than 4000.

Examples

			6! + 6!! + 1 = 769, which is prime.
		

Links

• Joe McLean, Interesting Sources of Probable Primes

Crossrefs

Cf. A000142, A006882, A116897.

Extensions

a(8) from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008

a(9) from Michael S. Branicky, Nov 15 2024