A280710 - OEIS

%I #23 Nov 20 2017 05:36:37

%S 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,

%T 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,

%U 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

%N Characteristic function of squarefree semiprimes.

%H Antti Karttunen, <a href="/A280710/b280710.txt">Table of n, a(n) for n = 1..65537</a>

%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>

%H <a href="/index/Eu#epf">Index entries for sequences computed from exponents in factorization of n</a>

%F 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).

%F a(n) = A008966(n)*A064911(n). - _Felix Fröhlich_, Jan 07 2017

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

%t Table[If[PrimeOmega[n] MoebiusMu[n]^2 == 2, 1, 0], {n, 1, 90}] (* _Indranil Ghosh_, Mar 10 2017 *)

%o (PARI) a(n) = bigomega(n)==2*issquarefree(n) \\ _Felix Fröhlich_, Jan 07 2017

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

%K nonn,easy

%O 1

%A _Wesley Ivan Hurt_, Jan 07 2017

%E More terms from _Antti Karttunen_, Nov 20 2017