A280710 Characteristic function of squarefree semiprimes.

0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Offset

1

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Index entries for characteristic functions

Index entries for sequences computed from exponents in factorization of n

Formula

a(n) = floor(Omega(n)*mu(n)^2/2)*floor(2*mu(n)^2/Omega(n)) for n>1 with a(1) = 0 where Omega(n) = A001222(n) and mu(n) = A008683(n).

a(n) = A008966(n)*A064911(n). - Felix Fröhlich, Jan 07 2017

Maple

with(numtheory): A280710:=n->`if`(bigomega(n)*mobius(n)^2 = 2, 1, 0): seq(A280710(n), n=1..100);

Mathematica

Table[If[PrimeOmega[n] MoebiusMu[n]^2 == 2, 1, 0], {n, 1, 90}] (* Indranil Ghosh, Mar 10 2017 *)

Prog

(PARI) a(n) = bigomega(n)==2*issquarefree(n) \\ Felix Fröhlich, Jan 07 2017

Crossrefs

Cf. A001222, A006881, A008683, A008966, A064911.

Sequence in context: A354981 A231600 A347579 * A354353 A353669 A363915

Adjacent sequences: A280707 A280708 A280709 * A280711 A280712 A280713

Keyword

nonn,easy

Author

Wesley Ivan Hurt, Jan 07 2017

Extensions

More terms from Antti Karttunen, Nov 20 2017

Status

approved