OFFSET
1,4
COMMENTS
a(n) = number of partitions of the set of divisors of n into two subsets U and V such that min(U) < min(V) and product(V) divides product(U). [Reinhard Zumkeller, Apr 05 2012]
It would appear that a(n) depends only on n's prime signature. - Charlie Neder, Oct 02 2018
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
Reinhard Zumkeller, Example for n = 120
FORMULA
EXAMPLE
For n = 6 there are 5 possibilities: 1*2*3*6=36, 1/2*3*6=9, 1*2/3*6=4, 1/2/3*6=1, 1*2*3/6=1 For n = 18 there are 13 possibilities: 1*2*3*6*9*18 1/2*3*6*9*18 1*2/3*6*9*18 1*2*3/6*9*18 1*2*3*6/9*18 1*2*3*6*9/18 1/2/3*6*9*18 1/2/3*6/9*18 1/2*3*6/9*18 1*2/3/6*9*18 1*2/3*6/9*18 1*2/3*6*9/18 1*2*3/6/9*18
PROG
(Haskell)
import Data.List (subsequences, (\\))
a060448 n = length [us | let ds = a027750_row n,
us <- init $ tail $ subsequences ds,
let vs = ds \\ us, head us < head vs,
product us `mod` product vs == 0] + 1
-- Reinhard Zumkeller, Apr 05 2012
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
Naohiro Nomoto, Apr 14 2001
STATUS
approved