OFFSET
1,1
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
a(1) = -1 since 6 = 2*3 and 3 = 2*2 - 1.
a(4) = +1 since 21 = 3*7 and 7 = 2*3 + 1.
PROG
(PARI) list(x)=my(v=List()); forprime(p=2, (sqrtint(x\1*8+1)+1)\4, if(isprime(2*p-1), listput(v, -1)); if(isprime(2*p+1), listput(v, 1))); Vec(v) \\ Charles R Greathouse IV, Jun 13 2013
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Greg Huber, Jul 28 2006
EXTENSIONS
Terms corrected by Charles R Greathouse IV, Jun 13 2013
STATUS
approved