A026785 a(n) = T(2n-1, n-2), T given by A026780.

1, 9, 60, 361, 2076, 11672, 64842, 357897, 1968788, 10813804, 59372770, 326086492, 1792293014, 9861375614, 54324086446, 299651439321, 1655124211372, 9154654655044, 50704627346170, 281214708137032, 1561706813618886

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-1, 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-1, 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-1, n-2) for n in (2..30)] # G. C. Greubel, Nov 02 2019

Crossrefs

Cf. A026780, A026781, A026782, A026783, A026784, A026786, A026787, A026788, A026789, A026790.

Sequence in context: A241976 A082150 A385563 * A153820 A390418 A009139

Adjacent sequences: A026782 A026783 A026784 * A026786 A026787 A026788

Keyword

nonn

Author

Clark Kimberling

Status

approved