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A202426 Numbers n such that  n!*n!! - 1 is prime. 1
2, 3, 4, 10, 11, 13, 17, 22, 26, 36, 79, 196 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

No additional terms up to n=1000. - Harvey P. Dale, Oct 29 2016

LINKS

Table of n, a(n) for n=1..12.

EXAMPLE

for n = 4, 4!*4!! + 1 = 24*8 - 1 = 191 is prime.

MATHEMATICA

lst={}; Do[If[PrimeQ[n!*n!!-1], AppendTo[lst, n]], {n, 500}]; lst

Select[Range[200], PrimeQ[#!#!!-1]&] (* Harvey P. Dale, Oct 29 2016 *)

PROG

(MAGMA) a:=func< n | Factorial(n)*(&*[n..2 by -2])-1 >; [ n: n in [0..660] | IsPrime(a(n)) ];  // Bruno Berselli, Dec 19 2011

CROSSREFS

Cf. A000142, A006882, A202424 (associated primes).

Sequence in context: A080897 A117383 A047455 * A039002 A295393 A120023

Adjacent sequences:  A202423 A202424 A202425 * A202427 A202428 A202429

KEYWORD

nonn

AUTHOR

Michel Lagneau, Dec 19 2011

STATUS

approved

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Last modified February 27 12:22 EST 2020. Contains 332306 sequences. (Running on oeis4.)