OFFSET
1,4
COMMENTS
An ordered factorization of n is a sequence of 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)).
LINKS
EXAMPLE
The ordered factorizations for n = 4, 8, 12, 16, 24, 32, 36:
4 8 12 16 24 32 36
2*2 4*2 6*2 4*4 12*2 8*4 6*6
2*2*2 2*2*3 8*2 2*2*6 16*2 12*3
3*2*2 2*2*4 3*2*4 2*2*8 18*2
2*4*2 4*2*3 2*4*4 2*2*9
4*2*2 6*2*2 4*2*4 2*3*6
2*2*2*2 4*4*2 2*6*3
8*2*2 3*2*6
2*2*4*2 3*3*4
4*2*2*2 3*6*2
2*2*2*2*2 4*3*3
6*2*3
6*3*2
9*2*2
2*2*3*3
2*3*3*2
3*2*2*3
3*3*2*2
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[Join@@Permutations/@facs[n], IntegerQ[altprod[#]]&]], {n, 100}]
PROG
(PARI) A347463(n, m=n, ap=1, e=0) = if(1==n, if(e%2, 1==denominator(ap), 1==numerator(ap)), sumdiv(n, d, if(d>1, A347463(n/d, d, ap * d^((-1)^e), 1-e)))); \\ Antti Karttunen, Jul 28 2024
CROSSREFS
Positions of 2's are A001248.
Positions of 1's are A005117.
The restriction to powers of 2 is A116406.
The even-length case is A347048
The odd-length case is A347049.
A046099 counts factorizations with no alternating permutations.
A273013 counts ordered factorizations of n^2 with alternating product 1.
A347438 counts factorizations with alternating product 1.
A347460 counts possible alternating products of factorizations.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Oct 07 2021
EXTENSIONS
Data section extended up to a(100) by Antti Karttunen, Jul 28 2024
STATUS
approved