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A028422 Number of ways n can be properly factored. 27
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
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.
Sequence in context: A294904 A055212 A360661 * A064577 A322435 A113949
KEYWORD
nonn
AUTHOR
Glen Burch (gburch(AT)erols.com)
STATUS
approved

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Last modified February 22 08:52 EST 2024. Contains 370248 sequences. (Running on oeis4.)