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 A117141 Primes of the form n!! - 1. 52
 2, 7, 47, 383, 10321919, 51011754393599, 1130138339199322632554990773529330319359999999, 73562883979319395645666688474019139929848516028923903999999999 (list; graph; refs; listen; history; text; internal format)
 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!<

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Last modified September 20 12:28 EDT 2019. Contains 327231 sequences. (Running on oeis4.)