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 A286782 Triangle T(n,k) read by rows: coefficients of polynomials P_n(t) defined in Formula section. 17
 1, 1, 6, 3, 50, 45, 5, 518, 637, 161, 7, 6354, 9567, 3744, 414, 9, 89782, 156123, 80784, 14850, 880, 11, 1435330, 2781389, 1749969, 446706, 46150, 1651, 13, 25625910, 54043365, 39305685, 12641265, 1877925, 121275, 2835, 15, 505785122, 1141864959, 928825464, 354665628, 68167144, 6500086, 281792, 4556, 17, 10944711398, 26137086451, 23244466392, 10134495804, 2361060574, 297418362, 19443460, 595764, 6954, 19 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS 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 vertex function in a many-body theory of fermions with two-body interaction (see Molinari link). LINKS Gheorghe Coserea, Rows n=0..123, flattened Luca G. Molinari, Hedin's equations and enumeration of Feynman's diagrams, arXiv:cond-mat/0401500 [cond-mat.str-el], 2005. FORMULA A(x;t) = Sum_{n>=0} P_n(t)*x^n = 1 + x*s + 2*x^2 * deriv(s,x), where s(x;t) = A286781(x;t) and P_n(t) = Sum_{k=0..n-1} T(n,k)*t^k for n>0. T(n+1,k) = (2*n+1)*A286781(n,k), A005416(n)=T(n,0), A088218(n)=P_n(-1). EXAMPLE A(x;t) = 1 + x + (6 + 3*t)*x^2 + (50 + 45*t + 5*t^2)*x^3 + ... Triangle starts: n\k  [0]       [1]       [2]       [3]       [4]      [5]     [6]    [7] [0]  1; [1]  1; [2]  6,        3; [3]  50,       45,       5; [4]  518,      637,      161,      7; [5]  6354,     9567,     3744,     414,      9; [6]  89782,    156123,   80784,    14850,    880,     11; [7]  1435330,  2781389,  1749969,  446706,   46150,   1651,   13; [8]  25625910, 54043365, 39305685, 12641265, 1877925, 121275, 2835,  15; [9]  ... MATHEMATICA 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_] := (2n+1) CoefficientList[Coefficient[y0[x, t], x, n], t]; T[0, 0] = 1; T[n_, k_] := row[n-1][[k+1]]; Table[T[n, k], {n, 0, max}, {k, 0, If[n == 0, 0, n-1]}] // Flatten (* Jean-François Alcover, May 19 2017, adapted from PARI *) PROG (PARI) A286781_ser(N, t='t) = {   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; }; A286782_ser(N, t='t) = my(s=A286781_ser(N, t)); 1 + x*s + 2*x^2 * deriv(s, 'x); concat(apply(p->Vecrev(p), Vec(A286782_ser(10)))) CROSSREFS Sequence in context: A229130 A349492 A088390 * A054380 A348171 A348142 Adjacent sequences:  A286779 A286780 A286781 * A286783 A286784 A286785 KEYWORD nonn,tabf AUTHOR Gheorghe Coserea, May 14 2017 STATUS approved

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Last modified December 8 17:01 EST 2021. Contains 349596 sequences. (Running on oeis4.)