A086288 - OEIS

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A086288

Number of distinct prime factors of 7-smooth numbers.

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,6

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from G. C. Greubel)

FORMULA

a(n) = A001221(A002473(n)).

a(n) <= 4.

MATHEMATICA

PrimeNu[Select[Range[500], Max[Transpose[FactorInteger[#]][[1]]] <= 7 &]] (* G. C. Greubel, May 09 2017 *)

CROSSREFS

Cf. A001221, A002473, A086289, A086290.