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A105555
Let d = number of divisors of n; a(n) = d-th prime.
3
2, 3, 3, 5, 3, 7, 3, 7, 5, 7, 3, 13, 3, 7, 7, 11, 3, 13, 3, 13, 7, 7, 3, 19, 5, 7, 7, 13, 3, 19, 3, 13, 7, 7, 7, 23, 3, 7, 7, 19, 3, 19, 3, 13, 13, 7, 3, 29, 5, 13, 7, 13, 3, 19, 7, 19, 7, 7, 3, 37, 3, 7, 13, 17, 7, 19, 3, 13, 7, 19, 3, 37, 3, 7, 13, 13, 7, 19, 3, 29, 11, 7, 3, 37, 7, 7, 7, 19, 3
OFFSET
1,1
LINKS
FORMULA
a(n) = A000040(A000005(n)). - Antti Karttunen, May 25 2017
EXAMPLE
n = 6 has 4 divisors, prime(4) = 7, so a(6) = 7.
MATHEMATICA
Prime[DivisorSigma[0, Range[90]]] (* Harvey P. Dale, Jul 27 2011 *)
PROG
(PARI) d(n) = for(x=1, n, print1(prime(numdiv(x))", "))
(Python)
from sympy import prime, divisor_count
def a(n): return prime(divisor_count(n)) # Indranil Ghosh, May 25 2017
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, May 03 2005
STATUS
approved