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%I #5 Mar 31 2012 10:32:35
%S 1,0,5,1,21,8,84,45,330,221,1287,1015,5006,4488,19465,19380,75753,
%T 82365,295261,346104,1152944,1442101,4510830,5969561,17682795,
%U 24582663,69448446,100804436,273241161,411921832,1076832989
%N Number of walks of length n between two nodes at distance 3 in the cycle graph C_9.
%C In general 2^n/m*Sum(r,0,m-1,Cos(2Pi*k*r/m)Cos(2Pi*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=3.
%F a(n)= 2^n/9*Sum(r, 0, 8, Cos(2Pi*r/3)Cos(2Pi*r/9)^n) G.f.: (-1+x)x^3/((1+x)(-1+2x)(1-3x^2+x^3)) a(n)=a(n-1)+5a(n-2)-4a(n-3)-5a(n-4)+2a(n-5)
%K nonn
%O 3,3
%A _Herbert Kociemba_, Jul 03 2004
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