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

Author

Jason Earls, Oct 31 2001

Keywords

• easy
• sign

Links

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

Crossrefs

Cf. A000720, A065358.

Programs

Mathematica

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

PARI

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