A114995 Numbers k such that the sum of the first k double factorials (1!! + 2!! + ... + k!!) is prime.

2, 5, 9, 10, 13, 14, 22, 25, 50, 66, 125, 250, 293, 314, 349, 1622, 1642, 2937, 2966, 3841, 4298, 4898, 5270

Offset

1,1

Comments

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

Links

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

Example

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

Crossrefs

Cf. A114410, A079078.

Sequence in context: A055394 A078360 A372886 * A047619 A046711 A376848

Adjacent sequences: A114992 A114993 A114994 * A114996 A114997 A114998

Keyword

nonn

Author

Giovanni Resta, Feb 23 2006

Extensions

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

Status

approved