A260235 Number of distinct prime factors of the n-th hexagonal number (A000384).

2, 2, 2, 2, 3, 2, 3, 2, 3, 3, 3, 2, 3, 3, 2, 3, 4, 2, 4, 3, 3, 3, 3, 2, 4, 2, 4, 3, 4, 2, 3, 4, 3, 4, 3, 2, 4, 4, 3, 2, 4, 3, 4, 3, 4, 3, 4, 2, 4, 3, 3, 4, 3, 3, 4, 3, 4, 3, 5, 2, 4, 3, 2, 4, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 3, 4, 5, 2, 4, 3, 3, 4, 4, 3, 4, 3

Offset

2,1

Links

Colin Barker, Table of n, a(n) for n = 2..1000

Formula

a(n) = A001221(A000384(n)).

Example

a(6) = 3 because A000384(6) = 66 = 2 * 3 * 11.

Mathematica

PrimeNu[PolygonalNumber[6, Range[2, 90]]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jun 23 2017 *)

Prog

(PARI)
pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number
a(n) = omega(pg(6, n))

Crossrefs

Cf. A000384, A001221, A260233, A260234, A260236.

Sequence in context: A262095 A163374 A108502 * A078120 A057525 A331362

Adjacent sequences: A260232 A260233 A260234 * A260236 A260237 A260238

Keyword

nonn

Author

Colin Barker, Jul 20 2015

Status

approved