A079249 Sum of r in all pairs (r,s), 0<=r<s, r+s divides n.

0, 0, 1, 1, 3, 4, 6, 7, 11, 13, 15, 20, 21, 27, 32, 35, 36, 50, 45, 59, 62, 70, 66, 92, 81, 99, 102, 119, 105, 150, 120, 155, 152, 172, 162, 219, 171, 216, 212, 255, 210, 296, 231, 302, 295, 319, 276, 396, 306, 391, 362, 425, 351, 492, 396, 503, 452, 511, 435, 646

Offset

1,5

Links

Table of n, a(n) for n=1..60.

Formula

G.f.: Sum_{n>1} x^(3*n)/(1-x^n)/(1-x^(2*n))^2.

a(n) = (1/2) * Sum_{d|n} ceiling(d/2) * (ceiling(d/2) - 1). - Sean A. Irvine, Aug 04 2025

Example

There are 7 pairs (r,s), 0<=r<s, such that p+q divides 6: (0,1), (0,2), (0,3), (0,6), (1, 2), (1, 5), (2, 4); thus a(6) = 0+0+0+0+1+1+2=4.

Crossrefs

Cf. A008805.

Sequence in context: A345716 A011975 A202112 * A374981 A306678 A075434

Adjacent sequences: A079246 A079247 A079248 * A079250 A079251 A079252

Keyword

easy,nonn

Author

Vladeta Jovovic, Feb 03 2003

Status

approved