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

Offset: 1

Author

Reinhard Zumkeller, Jul 15 2003

Keywords

• nonn

Links

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

Crossrefs

Cf. A001221, A002473, A086289, A086290.

Programs

Mathematica

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

Formula

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

a(n) <= 4.