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

1,3

Comments

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

Links

Table of n, a(n) for n=1..9.

Joe McLean, Interesting Sources of Probable Primes

Example

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

Crossrefs

Cf. A000142, A006882, A116897.

Sequence in context: A179330 A066864 A181737 * A061062 A375528 A270141

Adjacent sequences: A116893 A116894 A116895 * A116897 A116898 A116899

Keyword

hard,more,nonn

Author

Giovanni Resta, Mar 04 2006

Extensions

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

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

Status

approved