A338714 - OEIS

%I #16 Oct 15 2023 01:38:33

%S 0,0,0,1,1,2,1,1,3,2,2,1,2,2,2,1,2,1,2,1,2,2,2,0,8,2,1,1,3,0,3,1,2,2,

%T 2,0,3,2,2,0,3,0,3,1,1,2,3,0,14,1,2,1,4,0,2,0,2,2,4,0,4,2,1,0,2,0,4,1,

%U 2,0,4,0,4,2,1,1,2,0,4,0,1,2,4,0,2,2,2,0,4,0,2,1,2,2,2

%N Number of numbers of the form i*n with 1 <= i <= n and tau(i*n) = 6.

%H Seiichi Manyama, <a href="/A338714/b338714.txt">Table of n, a(n) for n = 1..10000</a>

%o (PARI) a(n) = sum(i=1, n, numdiv(i*n)==6); \\ _Michel Marcus_, Nov 11 2020

%o (Python)

%o from collections import Counter

%o from sympy import factorint

%o def A338714(n):

%o     f = Counter(factorint(n))

%o     return sum(1 for i in range(1,n+1) if (l:=tuple(sorted((f+Counter(factorint(i))).values())))==(1,2) or l==(5,)) # _Chai Wah Wu_, Oct 14 2023

%Y tau is A000005.

%Y For tau(i*n) = 2, 3, 4, see A010051, A296084, A338713.

%Y Inspired by A333995.

%K nonn

%O 1,6

%A _N. J. A. Sloane_, Nov 11 2020