A076185 Numbers n such that n!! + 2 is prime.

0, 1, 3, 5, 7, 9, 21, 23, 27, 57, 75, 103, 169, 219, 245, 461, 695, 1169, 3597, 3637, 7495, 27743, 28799, 32501

Offset: 1

Author

Zak Seidov, Nov 02 2002

Keywords

• nonn
• more

Comments

a(25) > 50000. - Robert Price, Jan 18 2015

a(1)=0 since 0!!=1 and 1+2 = 3 is prime. - Robert Price, Jan 18 2015

Links

• C. K. Caldwell, The Prime Glossary, Multifactorial prime
• C. Caldwell and H. Dubner (Eds): The top ten prime numbers: from the unpublished collections of R. Ondrejka (May 2001), Table 21 F, p. 75
• Ken Davis, Status of Search for Multifactorial Primes.
• Joe McLean, Interesting Sources of Probable Primes
• The OpenPFGW Project, Primality Tester

Crossrefs

Cf. A006882, A080778 and A076186, A076188, A076189, A076190, A076193, A076194, A076195, A076196, A076197 for other values of s in n!! + 2^s.

Programs

Mathematica

lst={};Do[If[PrimeQ[n!!+2], AppendTo[lst, n]], {n, 0, 13^3}];lst (* Vladimir Joseph Stephan Orlovsky, Sep 08 2008 *)
Select[Range[0,33000],PrimeQ[#!!+2]&] (* Harvey P. Dale, Jul 28 2017 *)

Extensions

Edited and extended (n<4096) by Hugo Pfoertner, Jun 19 2003

One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 30 2007

a(22) - a(23) from Robert Price, Oct 17 2012

a(24) from Robert Price, Jan 18 2015