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A271319 Number of distinct prime factors of the n-th n-gonal number (A060354). 4
1, 2, 1, 2, 3, 2, 2, 2, 3, 3, 3, 2, 3, 4, 2, 2, 3, 4, 3, 3, 3, 3, 3, 2, 4, 3, 3, 2, 5, 3, 2, 4, 3, 4, 3, 2, 4, 4, 4, 3, 4, 3, 3, 3, 3, 4, 3, 2, 4, 4, 4, 2, 4, 4, 3, 4, 3, 3, 4, 4, 3, 5, 2, 3, 4, 4, 4, 4, 4, 3, 4, 2, 4, 5, 3, 3, 4, 3, 4, 3, 4, 4, 5, 4, 3, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,2
LINKS
FORMULA
a(n) = A001221(A060354(n)).
EXAMPLE
a(7) = 2 because A060354(7) = 112 = 2^4 * 7^1.
MATHEMATICA
Table[PrimeNu[PolygonalNumber[n, n]], {n, 2, 90}] (* Harvey P. Dale, Sep 24 2023 *)
PROG
(PARI)
pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number
a(n) = omega(pg(n, n))
vector(100, n, n++; a(n))
CROSSREFS
Sequence in context: A233519 A192295 A037195 * A367404 A319178 A254041
KEYWORD
nonn
AUTHOR
Colin Barker, Apr 04 2016
STATUS
approved

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Last modified March 19 01:34 EDT 2024. Contains 370952 sequences. (Running on oeis4.)