A049421 Composite numbers k such that k!/k# - 1 is prime, where k# = primorial numbers A034386.

4, 6, 8, 16, 21, 34, 39, 45, 50, 72, 76, 133, 164, 202, 216, 221, 280, 496, 605, 2532, 2967, 3337, 8711, 10977, 13724, 15250, 18160, 20943, 33684, 41400

Offset

1,1

Comments

k!/k# is known as n compositorial.

Subset of A140293. Prime numbers are excluded since k!/k# = (k-1)!/(k-1)# when k is prime. - Giovanni Resta, Mar 28 2013

a(31) > 50000. - Roger Karpin, Jul 08 2015

Links

Table of n, a(n) for n=1..30.

Chris Caldwell, Compositorial

Mathematica

Primorial[n_] := Product[Prime[i], {i, 1, PrimePi[n]}];
Select[Range[2,
1000], ! PrimeQ[#] && PrimeQ[(#! / Primorial[#]) - 1] &] (* Robert Price, Oct 11 2019 *)

Crossrefs

Cf. A034386, A140293, A140294, A140315, A049420, A057017.

Sequence in context: A239412 A295006 A269833 * A260314 A238269 A039624

Adjacent sequences: A049418 A049419 A049420 * A049422 A049423 A049424

Keyword

hard,nonn

Author

Paul Jobling (paul.jobling(AT)whitecross.com)

Extensions

More terms from Robert G. Wilson v, Jun 21 2001

a(23)-a(25) from Giovanni Resta, Apr 02 2013

a(26) from Roger Karpin, Nov 29 2014

a(27)-a(28) from Daniel Heuer, ca Aug 2000

a(29)-a(30) from Serge Batalov, Feb 09 2015

Status

approved