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

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

Author

Reinhard Zumkeller, Apr 08 2003

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Cf. A072670.

Programs

Haskell

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

Formula

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