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A286783
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Triangle T(n,k) read by rows: coefficients of polynomials P_n(t) defined in Formula section.
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12
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1, 3, 15, 5, 105, 77, 7, 945, 1044, 234, 9, 10395, 14784, 5390, 550, 11, 135135, 227877, 113126, 19760, 1105, 13, 2027025, 3862305, 2371845, 586425, 58275, 1995, 15, 34459425, 71983440, 51607716, 16271380, 2356234, 147560, 3332, 17, 654729075, 1469813400, 1185214452, 446964322, 84487110, 7888876, 333564, 5244, 19, 13749310575, 32718512925, 28937407212, 12516198870, 2884205268, 358182846, 23006928, 690480, 7875, 21
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OFFSET
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0,2
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COMMENTS
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Row n>0 contains n terms.
T(n,k) is the number of Feynman's diagrams with k fermionic loops in the order n of the perturbative expansion in dimension zero for the polarization function in a many-body theory of fermions with two-body interaction (see Molinari link).
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LINKS
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FORMULA
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A(x;t) = Sum_{n>=0} P_n(t)*x^n = (1 + x*s + 2*x^2*deriv(s,x))/(1-x*s)^2, where s(x;t) = A286781(x;t) and P_n(t) = Sum_{k=0..n-1} T(n,k)*t^k for n>0.
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EXAMPLE
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A(x;t) = 1 + 3*x + (15 + 5*t)*x^2 + (105 + 77*t + 7*t^2)*x^3 + ...
Triangle starts:
n\k [0] [1] [2] [3] [4] [5] [6] [7]
[0] 1;
[1] 3;
[2] 15, 5;
[3] 105, 77, 7;
[4] 945, 1044, 234, 9;
[5] 10395, 14784, 5390, 550, 11;
[6] 135135, 227877, 113126, 19760, 1105, 13;
[7] 2027025, 3862305, 2371845, 586425, 58275, 1995, 15;
[8] 34459425, 71983440, 51607716, 16271380, 2356234, 147560, 3332, 17;
[9] ...
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MATHEMATICA
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max = 11; y0[x_, t_] = 1; y1[x_, t_] = 0; For[n = 1, n <= max, n++, y1[x_, t_] = (1 + x*y0[x, t] + 2*x^2*D[y0[x, t], x])*(1 - x*y0[x, t]*(1 - t))/(1 - x*y0[x, t])^2 + O[x]^n // Normal; y0[x_, t_] = y1[x, t] // Simplify];
s = y0[x, t];
se = (1 + x*s + 2*x^2*D[s, x])/(1 - x*s)^2 + O[x]^max // Normal;
row[n_] := row[n] = CoefficientList[Coefficient[se, x, n], t];
T[0, 0] = 1; T[n_, k_] := row[n][[k + 1]];
Table[T[n, k], {n, 0, max-1}, {k, 0, If[n == 0, 0, n-1]}] // Flatten (* Jean-François Alcover, May 19 2017, adapted from PARI *)
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PROG
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(PARI)
my(x='x+O('x^N), y0=1+O('x^N), y1=0, n=1);
while(n++,
y1 = (1 + x*y0 + 2*x^2*y0')*(1 - x*y0*(1-t))/(1-x*y0)^2;
if (y1 == y0, break()); y0 = y1; );
y0;
};
my(s=A286781_ser(N, t)); (1 + x*s + 2*x^2*deriv(s, 'x))/(1-x*s)^2;
};
concat(apply(p->Vecrev(p), Vec(A286783_ser(10))))
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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