1,1

At present the terms >= 2653 are only probable primes.

Zivkovic shows that all terms must be less than p=3612703, which divides a(n) for n>=p. - T. D. Noe (noe(AT)sspectra.com), Jan 25 2008

J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 160, p. 52, Ellipses, Paris 2008.

Martin Gardner, Strong Laws of Small Primes, in The Last Recreations, p. 198 (1997).

R. K. Guy, Unsolved Problems in Number Theory, B43.

M. Zivkovi\'c, The number of primes $ Sum\sp n\sb {i=1}(-1)\sp {n-i}i!$ is finite. Math. Comp. 68 (1999), no. 225, 403-409.

R. Ondrejka, The Top Ten: a Catalogue of Primal Configurations

Titanix, Primality proof for n=661

Eric Weisstein's World of Mathematics, Factorial Sums

Eric Weisstein's World of Mathematics, Integer Sequence Primes

Index entries for sequences related to factorial numbers

Eric Weisstein's World of Mathematics, Alternating Factorial

with(numtheory); f := proc(n) local i; add((-1)^(n-i)*i!, i=1..n); end; isprime(f(15));

Cf. A005165, A002981, A002982.

Cf. A100289.

Adjacent sequences: A001269 A001270 A001271 this_sequence A001273 A001274 A001275

Sequence in context: A066378 A125684 A089358 this_sequence A047563 A120561 A051016

nonn,hard,nice,fini

N. J. A. Sloane (njas(AT)research.att.com).

661 found independently by Eric Weisstein (eric(AT)weisstein.com) and Rachel Lewis (racheljlewis(AT)hotmail.com); 2653 and 3069 found independently by Chris Nash (nashc(AT)lexmark.com) and Rachel Lewis (racheljlewis(AT)hotmail.com).

3943, 4053, 4998 found by Paul Jobling (paul.jobling(AT)whitecross.com).

8275, 9158 found by team of Rachel Lewis, Paul Jobling and Chris Nash.

661!-660!+659!-... was shown to be prime by team of Giovanni La Barbera and others using the Certifix program developed by Marcel Martin, Jul 15 2000 (see link) - Paul Jobling (Paul.Jobling(AT)WhiteCross.com) and Giovanni La Barbera, Aug 02 2000

a(23)=11164 found by Paul Jobling on Nov 25 2004.

Edited by T. D. Noe (noe(AT)sspectra.com), Oct 30 2008