OFFSET
1,24
COMMENTS
A strict factorization of n is an increasing sequence of distinct positive integers > 1 with product n.
We define the alternating product of a sequence (y_1,...,y_k) to be Product_i y_i^((-1)^(i-1)).
All such factorizations must have odd length.
EXAMPLE
The a(720) = 30 factorizations:
(2*4*90) (3*4*60) (4*5*36) (5*6*24) (6*8*15) (8*9*10) (720)
(2*5*72) (3*5*48) (4*6*30) (5*8*18) (6*10*12)
(2*6*60) (3*6*40) (4*9*20) (5*9*16)
(2*8*45) (3*8*30) (4*10*18)
(2*9*40) (3*10*24) (4*12*15)
(2*10*36) (3*12*20)
(2*12*30) (3*15*16)
(2*15*24)
(2*18*20)
(2*3*120)
(2*3*4*5*6)
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
altprod[q_]:=Product[q[[i]]^(-1)^(i-1), {i, Length[q]}];
Table[Length[Select[facs[n], UnsameQ@@#&&altprod[#]>1&]], {n, 100}]
CROSSREFS
Allowing any alternating product gives A045778.
The reverse additive version (or restriction to powers of 2) is A067659.
The non-strict version is A339890.
Allowing equal parts and any alternating product < 1 gives A347440.
Allowing equal parts and any alternating product >= 1 gives A347456.
A046099 counts factorizations with no alternating permutations.
A273013 counts ordered factorizations of n^2 with alternating product 1.
A339846 counts even-length factorizations.
A347437 counts factorizations with integer alternating product.
A347441 counts odd-length factorizations with integer alternating product.
A347460 counts possible alternating products of factorizations.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 23 2021
STATUS
approved