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A214299
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Triangle d_k(n) read by rows: number of n-th order Feynman diagrams with k interactions, 0<=k<=n.
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3
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1, 2, 4, 24, 16, 80, 720, 288, 480, 3552, 40320, 11520, 11520, 28416, 271104, 3628800, 806400, 576000, 852480, 2711040, 31342080, 479001600, 87091200, 48384000, 51148800, 97597440, 376104960, 5087692800, 87178291200
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OFFSET
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0,2
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LINKS
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FORMULA
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d_k(n) = A214298(k)*binomial(n,k)*(2n-2k)!.
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EXAMPLE
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Triangle starts in row n=0 as:
1;
2, 4;
24, 16, 80;
720, 288, 480, 3552;
40320, 11520, 11520, 28416, 271104;
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MAPLE
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b:= proc(x, y, t) option remember; `if`(y>x or y<0, 0,
`if`(x=0, 1, b(x-1, y-1, false)*`if`(t, (x+y)/y, 1) +
b(x-1, y+1, true) ))
end:
T:= (n, k) -> k!*2^k*b(2*k, 0, false)*binomial(n, k)*(2*n-2*k)!:
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MATHEMATICA
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b[x_, y_, t_] := b[x, y, t] = If[y>x || y<0, 0, If[x == 0, 1, b[x-1, y-1, False] * If[t, (x+y)/y, 1] + b[x-1, y+1, True]]]; T[n_, k_] := k!*2^k*b[2*k, 0, False] * Binomial[n, k]*(2*n - 2*k)!; Table[Table[T[n, k], {k, 0, n}], {n, 0, 10}] // Flatten (* Jean-François Alcover, Jun 22 2015, after Alois P. Heinz *)
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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