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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!<<n-1), print1(", "t))) \\ Charles R Greathouse IV, Jun 16 2011

CROSSREFS

Cf. A002981, A002982, A088332.

Cf. A093173 = primes of the form (2^n * n!) - 1.

Sequence in context: A276649 A091117 A056854 * A305533 A125813 A254439

Adjacent sequences:  A117138 A117139 A117140 * A117142 A117143 A117144

KEYWORD

nonn

AUTHOR

Paolo P. Lava and Giorgio Balzarotti, Apr 21 2006

STATUS

approved

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