A026783 a(n) = T(2n, n-2), T given by A026780.

1, 11, 84, 557, 3446, 20514, 119336, 684227, 3886460, 21939528, 123347842, 691644044, 3871738018, 21652138770, 121026492186, 676391629701, 3780636102222, 21137831159462, 118234019051048, 661686074145618, 3705252204960252

Offset

2,2

Links

G. C. Greubel, Table of n, a(n) for n = 2..500

Maple

T:= proc(n, k) option remember;
    if n<0 then 0;
    elif k=0 or k =n then 1;
    elif k <= n/2 then
        procname(n-1, k-1)+procname(n-2, k-1)+procname(n-1, k) ;
    else
        procname(n-1, k-1)+procname(n-1, k) ;
    fi ;
end proc:
seq(T(2*n, n-2), n=2..30); # G. C. Greubel, Nov 02 2019

Mathematica

T[n_, k_]:= T[n, k]= If[n<0, 0, If[k==0 || k==n, 1, If[k<=n/2, T[n-1, k-1] + T[n-2, k-1] + T[n-1, k], T[n-1, k-1] + T[n-1, k] ]]];
Table[T[2*n, n-2], {n, 2, 30}] (* G. C. Greubel, Nov 02 2019 *)

Prog

(SageMath)
@CachedFunction
def T(n, k):
    if (n<0): return 0
    elif (k==0 or k==n): return 1
    elif (k<=n/2): return T(n-1, k-1) + T(n-2, k-1) + T(n-1, k)
    else: return T(n-1, k-1) + T(n-1, k)
[T(2*n, n-2) for n in (2..30)] # G. C. Greubel, Nov 02 2019

Crossrefs

Cf. A026780, A026781, A026782, A026784, A026785, A026786, A026787, A026788, A026789, A026790.

Sequence in context: A012478 A239461 A330966 * A244975 A379588 A271558

Adjacent sequences: A026780 A026781 A026782 * A026784 A026785 A026786

Keyword

nonn

Author

Clark Kimberling

Status

approved