|
|
A300902
|
|
a(n) = n! / Product_{p prime < n}.
|
|
2
|
|
|
1, 1, 2, 3, 4, 20, 24, 168, 192, 1728, 17280, 190080, 207360, 2695680, 2903040, 43545600, 696729600, 11844403200, 12541132800, 238281523200, 250822656000, 5267275776000, 115880067072000, 2665241542656000, 2781121609728000, 69528040243200000, 1807729046323200000
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,3
|
|
COMMENTS
|
Sum_{n >= 0} 1/a(n) = 3.1868081118360746...
|
|
LINKS
|
|
|
FORMULA
|
|
|
EXAMPLE
|
a(6) = 6! / Product_{p prime < 6} = 6 * 5 * 4 * 3 * 2/(5 * 3 * 2) = 6 * 4 = 24.
|
|
MAPLE
|
a:= n-> n!/mul(`if`(isprime(i), i, 1), i=1..n-1):
|
|
MATHEMATICA
|
Table[n!/(Times@@Prime[Range[PrimePi[n - 1]]]), {n, 0, 29}] (* Alonso del Arte, Mar 25 2018 *)
|
|
PROG
|
(PARI) a(n) = my(v=primes(primepi(n-1))); n!/prod(k=1, #v, v[k]); \\ Michel Marcus, Mar 15 2018
(Julia)
using Nemo
A300902(n) = div(fac(n), primorial(max(1, n-1)))
(Python)
from __future__ import division
from sympy import isprime
for n in range(1, 501):
m *= n
if isprime(n):
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|