cp's OEIS Frontend

A112753 Number of distinct prime factors of n-th number of the form 3^i*5^j.

%I A112753 #9 Feb 06 2020 07:14:56
%S A112753 0,1,1,1,2,1,1,2,2,1,1,2,2,1,2,2,1,2,1,2,2,2,2,1,1,2,2,2,2,1,2,2,2,1,
%T A112753 2,2,1,2,2,2,2,2,2,1,1,2,2,2,2,2,2,1,2,2,2,2,1,2,2,2,1,2,2,2,2,2,2,2,
%U A112753 2,1,1,2,2,2,2,2,2,2,2,1,2,2,2,2,2,1,2,2,2,2,1,2,2,2,2,2,2,2,2,2,2,1,1,2,2
%N A112753 Number of distinct prime factors of n-th number of the form 3^i*5^j.
%H A112753 Amiram Eldar, <a href="/A112753/b112753.txt">Table of n, a(n) for n = 1..10000</a>
%F A112753 a(n) = A001221(A003593(n)) = 2 - 0^A022336(n) + 0^A022337(n);
%F A112753 a(n) <= 2.
%t A112753 With[{nn=120},Take[PrimeNu/@Union[Flatten[{3^#[[1]] 5^#[[2]],5^#[[1]] 3^#[[2]]}&/@Tuples[Range[0,nn],2]]],nn]] (* _Harvey P. Dale_, Nov 29 2013 *)
%Y A112753 Cf. A001221, A003593, A022336, A022337, A086412, A112754, A112758.
%K A112753 nonn
%O A112753 1,5
%A A112753 _Reinhard Zumkeller_, Sep 18 2005