A027984 - OEIS

%I #10 Feb 25 2015 11:16:12

%S 1,6,20,58,161,436,1165,3088,8146,21426,56255,147538,386681,1013026,

%T 2653240,6948058,18193141,47634936,124717445,326526748,854877926,

%U 2238131506,5859556195,15340601158,40162350961,105146619486,275277778940

%N a(n) = Sum{T(n,k)*T(n,n+k)}, 0<=k<=n, T given by A027960.

%F Conjectures from _Colin Barker_, Feb 25 2015: (Start)

%F a(n) = 4*a(n-1)-3*a(n-2)-2*a(n-3)+a(n-4).

%F G.f.: (x-1)*(x+1)*(2*x+1) / ((x^2-3*x+1)*(x^2+x-1)).

%F (End)

%o (PARI) T027960(r,n) = if(r<0||n>2*r, return(0)); if(n==0||n==2*r, return(1)); if(n==1, 3, T027960(r-1, n-1)+T027960(r-1, n-2));

%o a(n) = sum(k=0, n, T027960(n, k)*T027960(n, n+k)); \\ _Michel Marcus_, Feb 25 2015

%K nonn

%O 0,2

%A _Clark Kimberling_