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A216175
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Number of all polyhedra (tetrahedra of any orientation and octahedra) of any size, formed when intersecting a regular tetrahedron by planes parallel to its sides and dividing its edges into n equal parts.
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3
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1, 6, 20, 50, 104, 193, 329, 526, 800, 1169, 1652, 2271, 3049, 4011, 5184, 6597, 8280, 10266, 12589, 15285, 18392, 21950, 26000, 30586, 35753, 41548, 48020, 55220, 63200, 72015, 81721, 92376, 104040, 116775, 130644, 145713, 162049, 179721, 198800, 219359
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = (1/288)*(7+9*(-1)^n-16*(-1)^(n mod 3)+24*n+124*n^2+104*n^3+22*n^4).
G.f.: x*(1+3*x+4*x^2+3*x^3)/((1+x)*(1+x+x^2)*(1-x)^5). - Bruno Berselli, Sep 11 2012
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EXAMPLE
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For n=3, the number of tetrahedra of any orientation and size is t(3)+t(1)=15+1=16 and the number of octahedra of any size is t(2)=4 the total number being a(n)=20, where t(n) denotes the tetrahedral number A000292(n).
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MATHEMATICA
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Table[(1/288) (7 + 9 (-1)^n - 16 (-1)^Mod[n, 3] + 24 n + 124 n^2 + 104 n^3 + 22 n^4), {n, 50}]
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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