A242456 Least number k such that n!/k is prime.

1, 2, 8, 24, 144, 720, 5760, 51840, 518400, 3628800, 43545600, 479001600, 6706022400, 100590336000, 1609445376000, 20922789888000, 376610217984000, 6402373705728000, 128047474114560000, 2688996956405760000, 59157933040926720000, 1124000727777607680000, 26976017466662584320000, 674400436666564608000000

Offset

2,2

Links

Jens Kruse Andersen, Table of n, a(n) for n = 2..1000

Formula

a(n) = n!/prime(pi(n)) = A000142(n)/A007917(n) for n > 1.

Maple

with(numtheory): A242456:=n->n!/ithprime(pi(n)): seq(A242456(n), n=2..30); # Wesley Ivan Hurt, Aug 17 2014

Mathematica

Table[n!/Prime[PrimePi[n]], {n, 2, 30}]  (* Wesley Ivan Hurt, Aug 17 2014 *)

Prog

(PARI)
vector(50, n, (n+1)!/(prime(primepi(n+1))))

Crossrefs

Cf. A000142, A007917.

Sequence in context: A176475 A145238 A093458 * A353779 A088994 A330505

Adjacent sequences: A242453 A242454 A242455 * A242457 A242458 A242459

Keyword

nonn,easy

Author

Derek Orr, Aug 16 2014

Status

approved