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A280210 Expansion of (Sum_{k>=1} mu(k)^2*x^k)^3, where mu(k) is the Moebius function (A008683). 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

Number of ordered ways of writing n as sum of three squarefree numbers (A005117).

LINKS

Table of n, a(n) for n=0..72.

Eric Weisstein's World of Mathematics, Squarefree

FORMULA

G.f.: (Sum_{k>=1} mu(k)^2*x^k)^3.

EXAMPLE

a(4) = 3 because we have [2, 1, 1], [1, 2, 1] and [1, 1, 2].

MATHEMATICA

nmax = 72; CoefficientList[Series[(Sum[MoebiusMu[k]^2 x^k, {k, 1, nmax}])^3, {x, 0, nmax}], x]

CROSSREFS

Cf. A005117, A008683, A098235.

Cf. A098238, A121550.

Sequence in context: A087916 A296693 A282585 * A023982 A189092 A287268

Adjacent sequences:  A280207 A280208 A280209 * A280211 A280212 A280213

KEYWORD

nonn

AUTHOR

Ilya Gutkovskiy, Dec 29 2016

STATUS

approved

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Last modified February 25 08:12 EST 2018. Contains 299646 sequences. (Running on oeis4.)