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 A027984 a(n) = Sum{T(n,k)*T(n,n+k)}, 0<=k<=n, T given by A027960. 0
 1, 6, 20, 58, 161, 436, 1165, 3088, 8146, 21426, 56255, 147538, 386681, 1013026, 2653240, 6948058, 18193141, 47634936, 124717445, 326526748, 854877926, 2238131506, 5859556195, 15340601158, 40162350961, 105146619486, 275277778940 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS FORMULA Conjectures from Colin Barker, Feb 25 2015: (Start) a(n) = 4*a(n-1)-3*a(n-2)-2*a(n-3)+a(n-4). G.f.: (x-1)*(x+1)*(2*x+1) / ((x^2-3*x+1)*(x^2+x-1)). (End) PROG (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)); a(n) = sum(k=0, n, T027960(n, k)*T027960(n, n+k)); \\ Michel Marcus, Feb 25 2015 CROSSREFS Sequence in context: A127982 A109164 A212689 * A018808 A027107 A247307 Adjacent sequences:  A027981 A027982 A027983 * A027985 A027986 A027987 KEYWORD nonn AUTHOR STATUS approved

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