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A286781
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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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18
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1, 2, 1, 10, 9, 1, 74, 91, 23, 1, 706, 1063, 416, 46, 1, 8162, 14193, 7344, 1350, 80, 1, 110410, 213953, 134613, 34362, 3550, 127, 1, 1708394, 3602891, 2620379, 842751, 125195, 8085, 189, 1, 29752066, 67168527, 54636792, 20862684, 4009832, 382358, 16576, 268, 1, 576037442, 1375636129, 1223392968, 533394516, 124266346, 15653598, 1023340, 31356, 366, 1
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OFFSET
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0,2
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COMMENTS
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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 self-energy 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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y(x;t) = Sum_{n>=0} P_n(t)*x^n satisfies y * (1-x*y)^2 = (1 + x*y + 2*x^2*deriv(y,x)) * (1 - x*y*(1-t)), with y(0;t) = 1, where P_n(t) = Sum_{k=0..n} T(n,k)*t^k, 0<=n, 0<=k<=n.
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EXAMPLE
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A(x;t) = 1 + (2 + t)*x + (10 + 9*t + t^2)*x^2 + (74 + 91*t + 23*t^2 + t^3)*x^3 + ...
Triangle starts:
n\k [0] [1] [2] [3] [4] [5] [6] [7] [8]
[0] 1;
[1] 2, 1;
[2] 10, 9, 1;
[3] 74, 91, 23, 1;
[4] 706, 1063, 416, 46, 1;
[5] 8162, 14193, 7344, 1350, 80, 1;
[6] 110410, 213953, 134613, 34362, 3550, 127, 1;
[7] 1708394, 3602891, 2620379, 842751, 125195, 8085, 189, 1;
[8] 29752066, 67168527, 54636792, 20862684, 4009832, 382358, 16576, 268, 1;
[9] ...
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MATHEMATICA
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max = 10; 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]];
row[n_] := CoefficientList[Coefficient[y0[x, t], x, n], t];
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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;
};
concat(apply(p->Vecrev(p), Vec(A286781_ser(10))))
\\ test: y = A286781_ser(50); y*(1-x*y)^2 == (1 + x*y + 2*x^2*deriv(y, 'x)) * (1 - x*y*(1-t))
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CROSSREFS
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For vertex and polarization functions see A286782 and A286783. For GWA of the self-energy and polarization functions see A286784 and A286785.
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KEYWORD
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AUTHOR
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STATUS
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approved
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