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a(n) = 1 if n is an even semiprime (2*prime), otherwise 0.
7

%I #9 Apr 22 2022 10:41:02

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

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

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

%N a(n) = 1 if n is an even semiprime (2*prime), otherwise 0.

%H Antti Karttunen, <a href="/A353478/b353478.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 If A000035(n) = 0, then a(n) = A010051(n/2), otherwise 0.

%F a(n) = A059841(n) * A064911(n).

%F a(n) = A064911(n) - A353480(n).

%o (PARI) A353478(n) = ((0==(n%2)) && isprime(n/2));

%Y Characteristic function of A100484, the primes doubled.

%Y Cf. A000035, A010051, A059841, A064911, A353477, A353479, A353480.

%K nonn

%O 1

%A _Antti Karttunen_, Apr 22 2022