A049420 Composite numbers n such that (n!/n#)+1 is prime, where n# = primorial numbers A034386.

4, 8, 14, 20, 26, 34, 56, 104, 153, 182, 194, 217, 230, 280, 462, 529, 1445, 2515, 3692, 6187, 6851, 13917, 17258, 48934

Offset

1,1

Comments

Note that n!/n# is known as n compositorial.

Subset of A140294. Prime numbers are excluded since n!/n# = (n-1)!/(n-1)# when n is prime. - Giovanni Resta, Mar 28 2013

a(23) > 14000. - Giovanni Resta, Apr 02 2013

a(25) > 50000. - Roger Karpin, Jul 07 2015

Links

Table of n, a(n) for n=1..24.

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, A049421.

Sequence in context: A274968 A317109 A173522 * A232996 A317292 A276221

Adjacent sequences: A049417 A049418 A049419 * A049421 A049422 A049423

Keyword

nonn,more

Author

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

Extensions

a(20) from Giovanni Resta, Mar 28 2013

a(21)-a(22) from Giovanni Resta, Apr 02 2013

a(23) from Roger Karpin, Nov 28 2014

a(24) from Roger Karpin, Jul 07 2015

Status

approved