A081757 Number of ways to write n as i*j+i-j, 0<i<j.

0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 3, 1, 2, 2, 2, 1, 3, 1, 2, 2, 3, 1, 3, 1, 3, 2, 2, 1, 4, 1, 2, 2, 4, 1, 3, 1, 3, 3, 2, 1, 4, 1, 3, 2, 3, 1, 4, 2, 3, 2, 2, 1, 6, 1, 2, 2, 3, 2, 4, 1, 3, 2, 4, 1, 5, 1, 2, 3, 3, 2, 4, 1, 4, 2, 2, 1, 6, 2, 2, 2, 4, 1, 5, 2, 3, 2, 2, 2, 6, 1, 3, 2, 4, 1, 4, 1, 4

Offset

1,11

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Formula

G.f.: Sum(x^(n^2+3*n)/(1-x^n),n = 1 .. infinity). - Vladeta Jovovic, May 13 2008

Example

n=25 = 2*23+2-23 = 3*11+3-11 = 4*7+4-7, therefore a(25)=3.

Prog

(Haskell)
a081757 n = length [() | j <- [2..n], i <- [1..j-1], i * j + i - j == n]
-- Reinhard Zumkeller, May 24 2013

Crossrefs

Cf. A072670.

Sequence in context: A363852 A357859 A338731 * A323880 A338651 A033107

Adjacent sequences: A081754 A081755 A081756 * A081758 A081759 A081760

Keyword

nonn

Author

Reinhard Zumkeller, Apr 08 2003

Status

approved