A028422 Number of ways n can be properly factored.

0, 0, 0, 1, 0, 1, 0, 2, 1, 1, 0, 3, 0, 1, 1, 4, 0, 3, 0, 3, 1, 1, 0, 6, 1, 1, 2, 3, 0, 4, 0, 6, 1, 1, 1, 8, 0, 1, 1, 6, 0, 4, 0, 3, 3, 1, 0, 11, 1, 3, 1, 3, 0, 6, 1, 6, 1, 1, 0, 10, 0, 1, 3, 10, 1, 4, 0, 3, 1, 4, 0, 15, 0, 1, 3, 3, 1, 4, 0, 11, 4, 1, 0, 10, 1, 1, 1, 6, 0, 10

Offset: 1

Author

Glen Burch (gburch(AT)erols.com)

Keywords

• nonn

Comments

a(n) = A066032(n,n-1) for n > 1; also number of ways to write n as a product with all factors <= n/2. - Reinhard Zumkeller, Oct 01 2012

Examples

			12 can be expressed as 2*6, 3*4 or 2*2*3, so a(12)=3.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

A001055(n) - 1.

Cf. A216599, A216600, A216601, A216602.

Programs

Haskell

a028422 1 = 0
a028422 n = (map (last . init) a066032_tabl) !! (n-1)
-- Reinhard Zumkeller, Oct 01 2012