A026784 a(n) = T(2n-1, n-1), T given by A026780.

1, 5, 24, 117, 580, 2916, 14834, 76221, 395048, 2063104, 10847078, 57373672, 305110106, 1630489090, 8751851866, 47166202181, 255128842340, 1384688987728, 7538592535170, 41159292861980, 225315261459390, 1236441650047554

Offset

1,2

Links

G. C. Greubel, Table of n, a(n) for n = 1..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-1), n=1..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-1], {n, 30}] (* G. C. Greubel, Nov 02 2019 *)

Prog

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

Crossrefs

Cf. A026780, A026781, A026782, A026783, A026785, A026786, A026787, A026788, A026789, A026790.

Sequence in context: A026707 A235115 A110190 * A017977 A017978 A291245

Adjacent sequences: A026781 A026782 A026783 * A026785 A026786 A026787

Keyword

nonn

Author

Clark Kimberling

Status

approved