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

1,1

Links

Antti Karttunen, Table of n, a(n) for n = 1..10000

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

Cf. A000005, A000040, A105560, A105561.

Sequence in context: A329277 A117531 A275940 * A066858 A333496 A152864

Adjacent sequences: A105552 A105553 A105554 * A105556 A105557 A105558

Keyword

easy,nonn

Author

Cino Hilliard, May 03 2005

Status

approved