A345446 Number of semiprime divisors of n whose square does not divide n.

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, 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, 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

Offset

1,12

Comments

a(p) = 0 for p prime.

Links

Table of n, a(n) for n=1..94.

Formula

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

Mathematica

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

Crossrefs

Cf. A001358, A056595.

Sequence in context: A242444 A236441 A327695 * A354911 A367098 A343660

Adjacent sequences: A345443 A345444 A345445 * A345447 A345448 A345449

Keyword

nonn

Author

Wesley Ivan Hurt, Jun 19 2021

Status

approved