A065357 a(n) = (-1)^pi(n) where pi(n) is the number of primes <= n.

1, 1, -1, 1, 1, -1, -1, 1, 1, 1, 1, -1, -1, 1, 1, 1, 1, -1, -1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, 1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, -1, -1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, 1, 1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, 1, 1

Offset

0,1

Links

N. J. A. Sloane, Table of n, a(n) for n = 0..10000 (First 1000 terms from Harry J. Smith)

Mathematica

(-1)^PrimePi[Range[0, 110]] (* Harvey P. Dale, Nov 02 2015 *)

Prog

(PARI) { for (n=0, 1000, if (n, a=(-1)^primepi(n), a=1); write("b065357.txt", n, " ", a) ) } \\ Harry J. Smith, Sep 30 2009

Crossrefs

Cf. A000720, A065358.

Sequence in context: A130151 A143431 A064179 * A119665 A121241 A122188

Adjacent sequences: A065354 A065355 A065356 * A065358 A065359 A065360

Keyword

easy,sign

Author

Jason Earls, Oct 31 2001

Status

approved