A086288 - OEIS

%I #16 Jan 06 2020 08:36:04

%S 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,

%T 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,

%U 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

%N Number of distinct prime factors of 7-smooth numbers.

%H Amiram Eldar, <a href="/A086288/b086288.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from G. C. Greubel)

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

%F a(n) <= 4.

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

%Y Cf. A001221, A002473, A086289, A086290.

%K nonn

%O 1,6

%A _Reinhard Zumkeller_, Jul 15 2003