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

1,6

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.

Sequence in context: A184341 A090455 A273190 * A104360 A318998 A079951

Adjacent sequences: A086285 A086286 A086287 * A086289 A086290 A086291

Keyword

nonn

Author

Reinhard Zumkeller, Jul 15 2003

Status

approved