A026761 a(n) = T(2n, n-2), T given by A026758.

1, 8, 48, 259, 1328, 6622, 32483, 157739, 761128, 3657815, 17534231, 83925062, 401363296, 1918822635, 9173429111, 43866599736, 209853869150, 1004463716937, 4810867131369, 23057388013314, 110588897473219, 530808778620583

Offset: 2

Author

Clark Kimberling

Keywords

• nonn

Links

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

Crossrefs

Cf. A026758, A026759, A026760, A026762, A026763, A026764, A026765, A026766, A026767, A026768.

Programs

Maple

T:= proc(n,k) option remember;
   if n<0 then 0;
   elif k=0 or k = n then 1;
   elif type(n,'odd') and k <= (n-1)/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) ;
   end if ;
end proc;
seq(T(2*n,n-2), n=2..30); # G. C. Greubel, Oct 31 2019

Mathematica

T[n_, k_]:= T[n, k]= If[n<0, 0, If[k==0 || k==n, 1, If[OddQ[n] && k<=(n - 1)/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, Oct 31 2019 *)

Sage

@CachedFunction
def T(n, k):
    if (n<0): return 0
    elif (k==0 or k==n): return 1
    elif (mod(n,2)==1 and k<=(n-1)/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, Oct 31 2019