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A347437
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Number of factorizations of n with integer alternating product.
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39
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1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 4, 1, 2, 1, 2, 1, 1, 1, 2, 2, 1, 2, 2, 1, 1, 1, 4, 1, 1, 1, 6, 1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 5, 2, 2, 1, 2, 1, 3, 1, 2, 1, 1, 1, 2, 1, 1, 2, 8, 1, 1, 1, 2, 1, 1, 1, 6, 1, 1, 2, 2, 1, 1, 1, 5, 4, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 2, 1, 1, 1, 6, 1, 2, 2, 6, 1, 1, 1, 2, 1, 1, 1, 7
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OFFSET
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1,4
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COMMENTS
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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)).
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LINKS
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FORMULA
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EXAMPLE
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The factorizations for n = 4, 16, 36, 48, 54, 64, 108:
(4) (16) (36) (48) (54) (64) (108)
(2*2) (4*4) (6*6) (2*4*6) (2*3*9) (8*8) (2*6*9)
(2*2*4) (2*2*9) (3*4*4) (3*3*6) (2*4*8) (3*6*6)
(2*2*2*2) (2*3*6) (2*2*12) (4*4*4) (2*2*27)
(3*3*4) (2*2*2*2*3) (2*2*16) (2*3*18)
(2*2*3*3) (2*2*4*4) (3*3*12)
(2*2*2*2*4) (2*2*3*3*3)
(2*2*2*2*2*2)
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MATHEMATICA
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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], IntegerQ@*altprod]], {n, 100}]
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PROG
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(PARI) A347437(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)&&(d<=m), A347437(n/d, d, ap * d^((-1)^e), 1-e)))); \\ Antti Karttunen, Oct 22 2023
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CROSSREFS
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Allowing any alternating product <= 1 gives A339846.
Allowing any alternating product > 1 gives A339890.
The restriction to powers of 2 is A344607.
The even-length case is A347438, also the case of alternating product 1.
Allowing any alternating product < 1 gives A347440.
Allowing any alternating product >= 1 gives A347456.
A046099 counts factorizations with no alternating permutations.
A071321 gives the alternating sum of prime factors of n (reverse: A071322).
A273013 counts ordered factorizations of n^2 with alternating product 1.
A347460 counts possible alternating products of factorizations.
Cf. A025047, A038548, A062312, A088218, A119620, A316523, A330972, A332269, A347445, A347447, A347451, A347454.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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