A321862 a(n) = A321857(prime(n)).

1, 2, 2, 3, 2, 3, 4, 3, 4, 3, 2, 3, 2, 3, 4, 5, 4, 3, 4, 3, 4, 3, 4, 3, 4, 3, 4, 5, 4, 5, 6, 5, 6, 5, 4, 3, 4, 5, 6, 7, 6, 5, 4, 5, 6, 5, 4, 5, 6, 5, 6, 5, 4, 3, 4, 5, 4, 3, 4, 3, 4, 5, 6, 5, 6, 7, 6, 7, 8, 7, 8, 7, 8, 9, 8, 9, 8, 9, 8, 7, 6, 5, 4, 5, 4, 5, 4

Offset

1,2

Comments

The first 10000 terms are positive, but conjecturally infinitely many terms should be negative.

The first negative term occurs at a(102091236) = -1. - Jianing Song, Nov 08 2019

Please see the comment in A321856 describing "Chebyshev's bias" in the general case.

Links

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

Wikipedia, Chebyshev's bias

Formula

a(n) = -Sum_{i=1..n} Legendre(prime(i),5) = -Sum_{primes p<=n} Kronecker(2,prime(i)) = -Sum_{i=1..n} A080891(prime(i)).

Example

prime(25) = 97, Pi(5,1)(97) = Pi(5,4)(97) = 5, Pi(5,2)(97) = Pi(5,3)(97) = 7, so a(25) = 7 + 7 - 5 - 5 = 4.

Prog

(PARI) a(n) = -sum(i=1, n, kronecker(5, prime(i)))

Crossrefs

Cf. A080891.

Let d be a fundamental discriminant.

Sequences of the form "a(n) = -Sum_{primes p<=n} Kronecker(d,p)" with |d| <= 12: A321860 (d=-11), A320857 (d=-8), A321859 (d=-7), A066520 (d=-4), A321856 (d=-3), A321857 (d=5), A071838 (d=8), A321858 (d=12).

Sequences of the form "a(n) = -Sum_{i=1..n} Kronecker(d,prime(i))" with |d| <= 12: A321865 (d=-11), A320858 (d=-8), A321864 (d=-7), A038698 (d=-4), A112632 (d=-3), this sequence (d=5), A321861 (d=8), A321863 (d=12).

Sequence in context: A131830 A147952 A091316 * A071825 A115727 A115726

Adjacent sequences: A321859 A321860 A321861 * A321863 A321864 A321865

Keyword

sign

Author

Jianing Song, Nov 20 2018

Extensions

Edited by Peter Munn, Nov 19 2023

Status

approved