A014202 Number of solutions to x^2 + x*y + y^2 <= n, excluding (0,0), divided by 6.

0, 1, 1, 2, 3, 3, 3, 5, 5, 6, 6, 6, 7, 9, 9, 9, 10, 10, 10, 12, 12, 14, 14, 14, 14, 15, 15, 16, 18, 18, 18, 20, 20, 20, 20, 20, 21, 23, 23, 25, 25, 25, 25, 27, 27, 27, 27, 27, 28, 31, 31, 31, 33, 33, 33, 33, 33, 35, 35, 35

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Crossrefs

A014201/6. Cf. A014200.

Programs

PARI

a(n)=if(n<1,0,sum(k=1,n,kronecker(k,3)*floor(n/k))) \\ Benoit Cloitre, Oct 31 2009

Formula

For n > 0, a(n) = Sum_{k=1..n} K(k,3)*floor(n/k) where K(x,y) is the Kronecker symbol. - Benoit Cloitre, Oct 31 2009