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A295935
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Number of twice-factorizations of n where the latter factorizations are constant, i.e., type (P,P,R).
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17
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1, 1, 1, 3, 1, 2, 1, 5, 3, 2, 1, 5, 1, 2, 2, 12, 1, 5, 1, 5, 2, 2, 1, 10, 3, 2, 5, 5, 1, 5, 1, 18, 2, 2, 2, 15, 1, 2, 2, 10, 1, 5, 1, 5, 5, 2, 1, 22, 3, 5, 2, 5, 1, 10, 2, 10, 2, 2, 1, 13, 1, 2, 5, 40, 2, 5, 1, 5, 2, 5, 1, 28, 1, 2, 5, 5, 2, 5, 1, 22, 12, 2, 1
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OFFSET
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1,4
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COMMENTS
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a(n) is also the number of ways to choose a perfect divisor of each factor in a factorization of n.
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LINKS
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FORMULA
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Dirichlet g.f.: 1/Product_{n > 1}(1 - A089723(n)/n^s).
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EXAMPLE
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The a(24) = 10 twice-factorizations are:
(2)*(2)*(2)*(3), (2)*(3)*(2*2), (3)*(2*2*2)
(2)*(2)*(6), (2*2)*(6),
(2)*(3)*(4),
(2)*(12),
(3)*(8),
(4)*(6),
(24).
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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]]}]];
Table[Sum[Product[Length[Divisors[GCD@@FactorInteger[d][[All, 2]]]], {d, f}], {f, facs[n]}], {n, 100}]
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CROSSREFS
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Cf. A000005, A001055, A052409, A052410, A089723, A279784, A281113, A284639, A295923, A295924, A295931.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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