A259651 Number of distinct prime factors of the n-th pentagonal number (A000326).

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

Offset

1,3

Links

Colin Barker, Table of n, a(n) for n = 1..1000

Formula

a(n) = A001221(A000326(n)).

Example

a(3) = 2 because A000326(3) = 12 = 2^2 * 3.

Prog

(PARI)
pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number
a(n) = omega(pg(5, n))

Crossrefs

Cf. A000326, A001221, A259649, A259650, A259652.

Sequence in context: A094915 A217619 A187186 * A253719 A081147 A236103

Adjacent sequences: A259648 A259649 A259650 * A259652 A259653 A259654

Keyword

nonn

Author

Colin Barker, Jul 02 2015

Status

approved