A116897 Numbers k such that k! - k!! + 1 is prime, where k!! denotes double factorial (A001147).

4, 6, 8, 14, 18, 28, 64, 324, 778, 882

Offset

1,1

Comments

Next term is greater than 3000.

Links

Table of n, a(n) for n=1..10.

Example

6! - 6!! + 1 = 673, which is prime.

Mathematica

Select[Range[900], PrimeQ[#!-#!!+1]&] (* Harvey P. Dale, Mar 27 2015 *)

Crossrefs

Cf. A000142, A001147, A116896.

Sequence in context: A173180 A200077 A256137 * A293763 A246324 A280227

Adjacent sequences: A116894 A116895 A116896 * A116898 A116899 A116900

Keyword

hard,more,nonn

Author

Giovanni Resta, Mar 04 2006

Status

approved