%I
%S 1,0,4,0,15,1,56,9,210,56,792,299,3003,1470,11441,6868,43776,31008,
%T 168151,136629,648208,591261,2507046,2523676,9726080,10656387,
%U 37839375,44612702,147600981,185477216,577147212,766744608,2261792303
%N Number of walks of length n between two nodes at distance 2 in the cycle graph C_9.
%C In general (2^n/m)*Sum_{r=0..m1} cos(2*Pi*k*r/m)*cos(2*Pi*r/m)^n) is the number of walks of length n between two nodes at distance k in the cycle graph C_m. Here we have m=9 and k=2.
%F a(n) = (2^n/9)*Sum_{r=0..8} cos(4*Pi*r/9)*cos(2*Pi*r/9)^n).
%F G.f.: x^2(1+x+x^2)/((1+x)*(1+2x)*(13x^2+x^3));
%F a(n) = a(n1) + 5*a(n2)  4*a(n3)  5*a(n4) + 2*a(n5).
%K nonn
%O 2,3
%A _Herbert Kociemba_, Jul 03 2004
