A355875 For n >= 1, k >= 1; a(n) = Sum_{k=1..n} f(n,k). f(n,k) = n*k/(n + k) if n*k divides (n+k), 0 otherwise.

0, 1, 0, 2, 0, 5, 0, 4, 0, 5, 0, 13, 0, 7, 6, 8, 0, 15, 0, 14, 0, 11, 0, 26, 0, 13, 0, 26, 0, 42, 0, 16, 0, 17, 10, 39, 0, 19, 0, 43, 0, 41, 0, 22, 38, 23, 0, 52, 0, 25, 0, 26, 0, 45, 0, 59, 0, 29, 0, 111, 0, 31, 14, 32, 0, 85, 0, 34, 0, 76, 0, 86, 0, 37, 30, 38

Offset: 1

Author

Ctibor O. Zizka, Jul 19 2022

Keywords

• nonn

Comments

a(n) = n/2 for n in A125499.

a(n) = 0 for n in A244579.

Examples

			n = 6; a(6) = Sum_{k=1..6} f(6,k) = 0 + 0 + 2 + 0 + 0 + 3 = 5.
		

Crossrefs

Cf. A005279, A125499, A244579.

Programs

Mathematica

a[n_] := Sum[If[Divisible[n*k, n + k], n*k/(n + k), 0], {k, 1, n}]; Array[a, 100] (* Amiram Eldar, Jul 21 2022 *)