A122810 Number of distinct prime factors of the smallest odd number with exactly n divisors.

0, 1, 1, 2, 1, 2, 1, 3, 2, 2, 1, 3, 1, 2, 2, 3, 1, 3, 1, 3, 2, 2, 1, 4, 2, 2, 3, 3, 1, 3, 1, 4, 2, 2, 2, 4, 1, 2, 2, 4, 1, 3, 1, 3, 3, 2, 1, 5, 2, 3, 2, 3, 1, 4, 2, 4, 2, 2, 1, 4, 1, 2, 3, 5, 2, 3, 1, 3, 2, 3, 1, 5, 1, 2, 3, 3, 2, 3, 1, 5, 4, 2, 1, 4, 2, 2, 2, 4, 1, 4, 2, 3, 2, 2, 2, 5, 1, 3, 3, 4, 1, 3, 1, 4, 3

Offset: 1

Author

Ray Chandler, Sep 22 2006

Keywords

• nonn

Comments

a(n) = 1 iff n is prime.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..2000 from Hans Havermann using the b-file of A038547 provided by _Don Reble_)

Crossrefs

Cf. A001221, A038547, A122375.

Programs

Mathematica

PrimeNu[Table[Select[Range[1, 532000, 2], DivisorSigma[0, #] == k + 1 &, 1], {k, 0, 15}] // Flatten] (* G. C. Greubel, May 07 2017 *)

Formula

a(n) = omega(A038547(n)), where omega(n) = A001221(n).

Extensions

Typo in A_number fixed by Matthew Vandermast, May 03 2014