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 A106549 a(n) = -1 if 2*n+1 is a prime, 1 if 2*n+1 is a prime squared, or 0 otherwise. 0

%I

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

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

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

%N a(n) = -1 if 2*n+1 is a prime, 1 if 2*n+1 is a prime squared, or 0 otherwise.

%e a(1)=0 because 1 is neither a prime nor a prime squared;

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

%e a(5)=1 because 9 = 3^2 is a prime squared.

%K easy,sign

%O 1,1

%A _Giovanni Teofilatto_, May 09 2005

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Last modified October 26 18:09 EDT 2020. Contains 338027 sequences. (Running on oeis4.)