A105555 Let d = number of divisors of n; a(n) = d-th prime.
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
Examples
n = 6 has 4 divisors, prime(4) = 7, so a(6) = 7.
Links
- Antti Karttunen, Table of n, a(n) for n = 1..10000
Programs
-
Mathematica
Prime[DivisorSigma[0,Range[90]]] (* Harvey P. Dale, Jul 27 2011 *)
-
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