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A114995
Numbers k such that the sum of the first k double factorials (1!! + 2!! + ... + k!!) is prime.
0
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
EXAMPLE
5 belongs since 1!! + 2!! + 3!! + 4!! + 5!! = 29, a prime.
CROSSREFS
Sequence in context: A055394 A078360 A372886 * A047619 A046711 A376848
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 23 2006
EXTENSIONS
a(18)-a(23) from Farideh Firoozbakht, May 16 2010
STATUS
approved