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A260235
Number of distinct prime factors of the n-th hexagonal number (A000384).
4
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
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
KEYWORD
nonn
AUTHOR
Colin Barker, Jul 20 2015
STATUS
approved