OFFSET
0,4
COMMENTS
a(n) is the number of proper divisors of factorial number A000142(n).
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
EXAMPLE
For n=4, 4! = 4*3*2*1 = 24, which has 7 proper divisors: 1, 2, 3, 4, 6, 8, and 12. So a(4) = 7. - Michael B. Porter, Aug 30 2016
MATHEMATICA
Table[DivisorSigma[0, n!] - 1, {n, 0, 50}] (* G. C. Greubel, Aug 30 2016 *)
PROG
(Magma) [DivisorSigma(0, Factorial(n)) - 1: n in [0..40]]; // Vincenzo Librandi, Aug 31 2016
(PARI) a(n) = numdiv(n!) - 1; \\ Michel Marcus, Aug 31 2016
(Python)
from sympy import factorial, divisor_count
def A153823(n):
return divisor_count(factorial(n))-1 # Chai Wah Wu, Aug 24 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Jan 02 2009
EXTENSIONS
More terms from Omar E. Pol, Jan 17 2009
STATUS
approved