A116896 - OEIS

%I #13 Nov 15 2024 14:49:25

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

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

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

%H Joe McLean, <a href="http://web.archive.org/web/20091027034731/http://uk.geocities.com/nassarawa%40btinternet.com/probprim.htm">Interesting Sources of Probable Primes</a>

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

%Y Cf. A000142, A006882, A116897.

%K hard,more,nonn

%O 1,3

%A _Giovanni Resta_, Mar 04 2006

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

%E a(9) from _Michael S. Branicky_, Nov 15 2024