%I #8 Dec 30 2012 17:10:52
%S 8,352,6568,92608,1143880,13115680,143509480,1521045376,15755283592,
%T 160392633568,1610896046632,16004345360704,157595696236744,
%U 1540370736608416,14961422399467624,144535575132212992,1389765142844188936,13308390999949846624,126980061472109030056,1207661435632198248640
%N The Wiener index of the Bethe cactus lattice graph C_n defined pictorially in the Hosoya - Balasubramanian reference.
%D K. Balasubramanian, Recent developments in tree-pruning methods and polynomials for cactus graphs and trees, J. Math. Chemistry, 4 (1990) 89-102.
%D H. Hosoya, K. Balasubramanian, Exact dimer statistics and characteristic polynomials of cacti lattices, Theor. Chim. Acta 76 (1989) 315-329.
%F a(n) = -2+3^(n-1)*28+3^(2*n-1)*(16*n-22).
%F G.f.: 8*x*(1+22*x+9*x^2)/((1-x)*(1-3*x)*(1-9*x)^2). - _Bruno Berselli_, Dec 30 2012
%p a := proc (n) options operator, arrow: -2+28*3^(n-1)+3^(2*n-1)*(16*n-22) end proc: seq(a(n), n = 1 .. 20);
%Y Cf. A221045.
%K nonn,easy
%O 1,1
%A _Emeric Deutsch_, Dec 30 2012