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A028422 Number of ways n can be properly factored. 20
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,8

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

LINKS

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

EXAMPLE

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

PROG

(Haskell)

a028422 1 = 0

a028422 n = (map (last . init) a066032_tabl) !! (n-1)

-- Reinhard Zumkeller, Oct 01 2012

CROSSREFS

A001055(n) - 1.

Cf. A216599, A216600, A216601, A216602.

Sequence in context: A114206 A073202 A055212 * A064577 A113949 A257991

Adjacent sequences:  A028419 A028420 A028421 * A028423 A028424 A028425

KEYWORD

nonn

AUTHOR

Glen Burch (gburch(AT)erols.com)

STATUS

approved

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Last modified October 24 06:43 EDT 2017. Contains 293836 sequences.