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A307939
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Number of (undirected) Hamiltonian paths in the n-dipyramidal graph.
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1
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36, 120, 310, 660, 1218, 2032, 3150, 4620, 6490, 8808, 11622, 14980, 18930, 23520, 28798, 34812, 41610, 49240, 57750, 67188, 77602, 89040, 101550, 115180, 129978, 145992, 163270, 181860, 201810, 223168, 245982, 270300, 296170, 323640, 352758, 383572, 416130, 450480
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OFFSET
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3,1
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LINKS
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FORMULA
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a(n) = 2*n*(31 - 20*n + 4*n^2) for n > 3.
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n > 7.
G.f.: 2*x^3*(18 - 12*x + 23*x^2 - 2*x^3 - 3*x^4) / (1 - x)^4. - Colin Barker, May 09 2019
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MATHEMATICA
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Join[{36}, Table[2 n (31 - 20 n + 4 n^2), {n, 4, 20}]]
Join[{36}, LinearRecurrence[{4, -6, 4, -1}, {120, 310, 660, 1218}, 20]]
CoefficientList[Series[-2 (-18 + 12 x - 23 x^2 + 2 x^3 + 3 x^4)/(-1 + x)^4, {x, 0, 20}], x]
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PROG
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(PARI) Vec(2*x^3*(18 - 12*x + 23*x^2 - 2*x^3 - 3*x^4) / (1 - x)^4 + O(x^40)) \\ Colin Barker, May 09 2019
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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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