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A093566
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a(n) = n*(n-1)*(n-2)*(n-3)*(n^2-3*n-2)/48.
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16
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0, 0, 0, 0, 1, 20, 120, 455, 1330, 3276, 7140, 14190, 26235, 45760, 76076, 121485, 187460, 280840, 410040, 585276, 818805, 1125180, 1521520, 2027795, 2667126, 3466100, 4455100, 5668650, 7145775, 8930376, 11071620, 13624345, 16649480, 20214480
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OFFSET
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0,6
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COMMENTS
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a(n+1) is the number of chiral pairs of colorings of the faces of a cube (vertices of a regular octahedron) using n or fewer colors. - Robert A. Russell, Sep 28 2020
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LINKS
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FORMULA
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a(n) = binomial(binomial(n-1, 2), 3).
G.f.: -x^4*(1+13*x+x^2)/(x-1)^7. - R. J. Mathar, Dec 08 2010
a(n+1) = 1*C(n,3) + 16*C(n,4) + 30*C(n,5) + 15*C(n,6), where the coefficient of C(n,k) is the number of chiral pairs of colorings using exactly k colors. - Robert A. Russell, Sep 28 2020
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EXAMPLE
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For a(3+1) = 1, each of the three colors is applied to a pair of adjacent faces of the cube (vertices of the octahedron). - Robert A. Russell, Sep 28 2020
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MATHEMATICA
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Table[ Binomial[ Binomial[n-1, 2], 3], {n, 0, 32}]
LinearRecurrence[{7, -21, 35, -35, 21, -7, 1}, {0, 0, 0, 0, 1, 20, 120}, 40] (* Harvey P. Dale, Feb 18 2016 *)
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PROG
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(Sage) [(binomial(binomial(n, 2), 3)) for n in range(-1, 33)] # Zerinvary Lajos, Nov 30 2009
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CROSSREFS
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a(n+1) = A325006(3,n) (chiral pairs of colorings of orthotope facets or orthoplex vertices.
a(n+1) = A337889(3,n) (chiral pairs of colorings of orthotope faces or orthoplex peaks).
(End)
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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