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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
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, 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, 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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..87.

EXAMPLE

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

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

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

CROSSREFS

Sequence in context: A242647 A167393 A275606 * A075897 A135947 A211487

Adjacent sequences:  A106546 A106547 A106548 * A106550 A106551 A106552

KEYWORD

easy,sign

AUTHOR

Giovanni Teofilatto, May 09 2005

STATUS

approved

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Last modified September 24 07:01 EDT 2020. Contains 337317 sequences. (Running on oeis4.)