A156660 - OEIS

A156660

Characteristic function of Sophie Germain primes.

0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1, 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, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 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, 0, 0, 0, 0

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OFFSET

0,1

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000

Wikipedia, Sophie Germain prime

Index entries for characteristic functions

FORMULA

a(n) = if n and also 2*n+1 is prime then 1 else 0.

a(A005384(n)) = 1; a(A138887(n)) = 0; a(A053176(n)) = 0.

A156874(n) = Sum_{k=1..n} a(k). - Reinhard Zumkeller, Feb 18 2009

a(n) = A010051(n)*A010051(2*n+1).