A089085 Numbers k such that (k! + 3)/3 is prime.

3, 5, 6, 8, 11, 17, 23, 36, 77, 93, 94, 109, 304, 497, 1330, 1996, 3027, 3053, 4529, 5841, 20556, 26558, 28167

Offset

1,1

Comments

a(21) > 20000. The PFGW program has been used to certify all the terms up to a(20), using the "N-1" deterministic test. - Giovanni Resta, Mar 31 2014

Links

Table of n, a(n) for n=1..23.

Mathematica

Select[Range[0, 1400], PrimeQ[(#!+3)/3] &] (* Vladimir Joseph Stephan Orlovsky, Apr 29 2008 *)

Prog

(Magma) [n: n in [0..500] | IsPrime((Factorial(n)+3) div 3)]; // Vincenzo Librandi, Dec 12 2011
(PARI) is(n)=ispseudoprime(n!\3+1) \\ Charles R Greathouse IV, Mar 21 2013

Crossrefs

Cf. A089131.

Cf. n!/m-1 is a prime: A002982, A082671, A139056, A139199-A139205; n!/m+1 is a prime: A002981, A082672, A089085, A139061, A139058, A139063, A139065, A151913, A137390, A139071 (1<=m<=10).

Sequence in context: A121501 A327218 A062832 * A033163 A228372 A039869

Adjacent sequences: A089082 A089083 A089084 * A089086 A089087 A089088

Keyword

nonn

Author

Cino Hilliard, Dec 05 2003

Extensions

More terms from Don Reble, Dec 06 2003

1330 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008

Typo in Mma program corrected by Vincenzo Librandi, Dec 12 2011

a(16)-a(20) from Giovanni Resta, Mar 31 2014

a(21)-a(23) from Serge Batalov, Feb 17 2015

Status

approved