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A347441 Number of odd-length factorizations of n with integer alternating product. 17
0, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 2, 2, 1, 1, 1, 4, 1, 1, 1, 4, 1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 5, 1, 2, 1, 2, 1, 3, 1, 2, 1, 1, 1, 2, 1, 1, 2, 5, 1, 1, 1, 2, 1, 1, 1, 6, 1, 1, 2, 2, 1, 1, 1, 5, 2, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 2, 1, 1, 1, 6, 1, 2, 2, 4, 1, 1, 1, 2, 1, 1, 1, 7 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,8
COMMENTS
A factorization of n is a weakly increasing 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
FORMULA
a(2^n) = A027193(n).
EXAMPLE
The a(n) factorizations for n = 2, 8, 32, 48, 54, 72, 108:
2 8 32 48 54 72 108
2*2*2 2*2*8 2*4*6 2*3*9 2*6*6 2*6*9
2*4*4 3*4*4 3*3*6 3*3*8 3*6*6
2*2*2*2*2 2*2*12 2*2*18 2*2*27
2*2*2*2*3 2*3*12 2*3*18
2*2*2*3*3 3*3*12
2*2*3*3*3
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], OddQ[Length[#]]&&IntegerQ[altprod[#]]&]], {n, 100}]
PROG
(PARI) A347441(n, m=n, ap=1, e=0) = if(1==n, (e%2)&&1==denominator(ap), sumdiv(n, d, if((d>1)&&(d<=m), A347441(n/d, d, ap * d^((-1)^e), 1-e)))); \\ Antti Karttunen, Oct 22 2023
CROSSREFS
The restriction to powers of 2 is A027193.
Positions of 1's are A167207 = A005117 \/ A001248.
Allowing any alternating product gives A339890.
Allowing even-length factorizations gives A347437.
The even-length instead of odd-length version is A347438.
The additive version is A347444, ranked by A347453.
A038548 counts possible reverse-alternating products of factorizations.
A273013 counts ordered factorizations of n^2 with alternating product 1.
A339846 counts even-length factorizations.
A347439 counts factorizations with integer reciprocal alternating product.
A347440 counts factorizations with alternating product < 1.
A347442 counts factorizations with integer reverse-alternating product.
A347456 counts factorizations with alternating product >= 1.
A347463 counts ordered factorizations with integer alternating product.
Sequence in context: A355150 A333915 A293234 * A360617 A102097 A361566
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 07 2021
EXTENSIONS
Data section extended up to a(108) by Antti Karttunen, Oct 22 2023
STATUS
approved

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Last modified March 28 22:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)