OFFSET
1,1
REFERENCES
G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 158.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..15
FORMULA
a(n) = A093173(n-1) for n>1. - Alexander Adamchuk, Apr 18 2007
EXAMPLE
6!! - 1 = 6*4*2 - 1 = 48 - 1 = 47, which is prime.
8!! - 1 = 8*6*4*2 - 1 = 384 - 1 = 383, which is prime.
MAPLE
SFACT:= proc(n) local i, j, k; for k from 1 by 1 to n do i:=k; j:=k-2; while j >0 do i:=i*j; j:=j-2; od: if isprime(i-1) then print(i-1); fi; od: end: SFACT(100);
MATHEMATICA
lst={}; Do[p=n!!-1; If[PrimeQ[p], AppendTo[lst, p]], {n, 0, 5!, 1}]; lst (* Vladimir Joseph Stephan Orlovsky, Jan 27 2009 *)
Select[Table[n!!-1, {n, 1, 100}], PrimeQ] (* Vincenzo Librandi, Dec 07 2011 *)
PROG
(PARI) print1(2); for(n=1, 1e3, if(ispseudoprime(t=n!<<n-1), print1(", "t))) \\ Charles R Greathouse IV, Jun 16 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava and Giorgio Balzarotti, Apr 21 2006
STATUS
approved