A345446 - OEIS

%I #27 Aug 10 2023 14:16:47

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

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

%U 1,3,0,2,0,1,2,2,1,3,0,1,0,1,0,4,1,1,1,2,0,4,1,2,1,1

%N Number of semiprime divisors of n whose square does not divide n.

%C a(p) = 0 for p prime.

%F a(n) = Sum_{d|n} [Omega(d) = 2] * (ceiling(n/d^2) - floor(n/d^2)), where [ ] is the Iverson bracket.

%t Table[Count[Select[Divisors[n],PrimeOmega[#]==2&],_?(!IntegerQ[n/#^2]&)],{n,120}] (* _Harvey P. Dale_, Aug 10 2023 *)

%Y Cf. A001358, A056595.

%K nonn

%O 1,12

%A _Wesley Ivan Hurt_, Jun 19 2021