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A081757
Number of ways to write n as i*j+i-j, 0<i<j.
4
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
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
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Apr 08 2003
STATUS
approved