1,1

a(18) must be greater than 2300. The sum of the first 1642 double factorials is a (probable) prime with 2286 digits.

Numbers corresponding to a(18)-a(23) are probable primes. - Farideh Firoozbakht, May 16 2010

Table of n, a(n) for n=1..23.

5 belongs since 1!! + 2!! + 3!! + 4!! + 5!! = 29, a prime.

Cf. A114410, A079078.

Sequence in context: A155469 A055394 A078360 * A047619 A046711 A191171

Adjacent sequences: A114992 A114993 A114994 * A114996 A114997 A114998

nonn

Giovanni Resta, Feb 23 2006

a(18)-a(23) from Farideh Firoozbakht, May 16 2010

approved