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A049421 Composite numbers n such that (n!/n#)-1 is prime, where n# = primorial numbers A034386. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

n!/n# is known as n compositorial.

Subset of A140293. Prime numbers are excluded since n!/n# = (n-1)!/(n-1)# when n 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.

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

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Last modified December 9 02:06 EST 2021. Contains 349625 sequences. (Running on oeis4.)