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A308122
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Sum of the perimeters of all scalene triangles with perimeter n whose side lengths are squarefree.
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0
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 13, 14, 30, 16, 0, 18, 0, 0, 21, 22, 69, 48, 0, 26, 54, 56, 116, 150, 217, 160, 99, 136, 210, 144, 148, 190, 273, 200, 164, 210, 301, 220, 405, 506, 611, 480, 441, 500, 459, 312, 530, 594, 550, 392, 342, 464, 531, 480, 732
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OFFSET
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1,13
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LINKS
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FORMULA
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a(n) = n * Sum_{k=1..floor((n-1)/3)} Sum_{i=k+1..floor((n-k-1)/2)} sign(floor((i+k)/(n-i-k+1))) * mu(i)^2 * mu(k)^2 * mu(n-i-k)^2, where mu is the Möbius function (A008683).
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MATHEMATICA
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Table[n*Sum[Sum[MoebiusMu[i]^2*MoebiusMu[k]^2*MoebiusMu[n - i - k]^2*Sign[Floor[(i + k)/(n - i - k + 1)]], {i, k + 1, Floor[(n - k - 1)/2]}], {k, Floor[(n - 1)/3]}], {n, 100}]
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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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