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A280210
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Expansion of (Sum_{k>=1} mu(k)^2*x^k)^3, where mu(k) is the Moebius function (A008683).
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10
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0, 0, 0, 1, 3, 6, 7, 9, 12, 19, 21, 21, 21, 30, 36, 37, 36, 48, 58, 63, 57, 70, 78, 87, 78, 96, 105, 114, 105, 123, 133, 138, 126, 148, 162, 174, 156, 195, 207, 220, 192, 234, 250, 261, 237, 280, 312, 318, 282, 330, 363, 370, 315, 375, 405, 432, 366, 421, 453, 483, 417, 468, 507, 532, 474, 537, 568, 591, 519, 601, 630, 666, 570
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OFFSET
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0,5
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COMMENTS
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Number of ordered ways of writing n as sum of three squarefree numbers (A005117).
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LINKS
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FORMULA
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G.f.: (Sum_{k>=1} mu(k)^2*x^k)^3.
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EXAMPLE
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a(4) = 3 because we have [2, 1, 1], [1, 2, 1] and [1, 1, 2].
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MATHEMATICA
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nmax = 72; CoefficientList[Series[(Sum[MoebiusMu[k]^2 x^k, {k, 1, nmax}])^3, {x, 0, nmax}], x]
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CROSSREFS
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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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