A353481 - OEIS

%I #15 Jan 27 2023 04:45:13

%S 0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,

%T 1,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,1,0,1,0,0,0,0,0,0,0,1,0,0,0,

%U 1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,1,0,0,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,1,0,0

%N a(n) = 1 if n is an odd squarefree semiprime, otherwise 0.

%H Antti Karttunen, <a href="/A353481/b353481.txt">Table of n, a(n) for n = 1..65537</a>

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

%F a(n) = A000035(n) * A280710(n).

%F a(n) = A008966(n) * A353480(n).

%F a(n) = A064911(n) * A323239(n).

%F For all n <> 4, a(n) = A353480(n) - A302048(n).

%F For all n >= 1, a(n) >= A353482(n) >= A353483(n).

%t Table[If[OddQ[n]&&PrimeOmega[n]==2&&SquareFreeQ[n],1,0],{n,130}] (* _Harvey P. Dale_, Aug 17 2022 *)

%o (PARI) A353481(n) = ((2==bigomega(n)) && (2==omega(n)) && (1==(n%2)));

%Y Characteristic function of A046388.

%Y Cf. A359465, A008966, A064911, A280710, A302048, A323239, A353480, A353482, A353483.

%K nonn

%O 1

%A _Antti Karttunen_, Apr 22 2022