0,1

Dario Alpern, Factorization using the Elliptic Curve Method.

a(7)=2521 because 7!/2!+1=2521 is prime, whereas 7!/1!+1=5041=71^2 is composite,

a(19)=2 because the only prime of the form 19!/k!+1 is 19!/19!+1=2.

Cf. A093621 smallest k>0 such that n!/k!+1 is prime, A002981 n!+1 is prime, A088332 primes of form n!+1.

Sequence in context: A167348 A068524 A109277 this_sequence A060357 A064714 A002848

Adjacent sequences: A093434 A093435 A093436 this_sequence A093438 A093439 A093440

nonn

Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Apr 01 2004

Corrected and extended by Hugo Pfoertner (hugo(AT)pfoertner.org), Apr 06 2004