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a(n) = 1 if n is an odd semiprime, otherwise 0.
11

%I #9 Apr 22 2022 10:41:06

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

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

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

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

%H Antti Karttunen, <a href="/A353480/b353480.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) * A064911(n).

%F a(n) = A353477(n) + A353479(n).

%F a(n) = A064911(n) - A353478(n).

%F For all n <> 4, a(n) = A302048(n) + A353481(n).

%e 15 = 3*5 is an odd semiprime, thus a(15) = 1.

%e 121 = 11*11 is an odd semiprime, thus a(121) = 1.

%o (PARI) A353480(n) = ((2==bigomega(n)) && (1==(n%2)));

%Y Characteristic function of A046315.

%Y Cf. A000035, A064911, A302048, A353477, A353478, A353479, A353481.

%K nonn

%O 1

%A _Antti Karttunen_, Apr 22 2022