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 A106667 a(n)= 1 iff prime + 2 is a prime, a(n)= -1 iff prime + 2 is a semiprime, otherwise 0. 0

%I

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

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

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

%N a(n)= 1 iff prime + 2 is a prime, a(n)= -1 iff prime + 2 is a semiprime, otherwise 0.

%e a(1)=-1 because 2 + 2 = 4 =2*2 is a semiprime;

%e a(2)=1 because 3 + 2 = 5 is a prime;

%e a(14)=0 because 43 + 2 = 45 is not prime neither semiprime.

%K easy,sign

%O 1,1

%A _Giovanni Teofilatto_, May 13 2005

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