A026760 a(n) = T(2n, n-1), T given by A026758.

1, 5, 23, 104, 469, 2119, 9607, 43727, 199819, 916631, 4220267, 19497608, 90370622, 420136173, 1958787580, 9156770130, 42912496696, 201579245739, 949002525067, 4477049676288, 21162505063028, 100217666089863, 475421115762173

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 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-1), n=1..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-1], {n, 0, 30}] (* G. C. Greubel, Oct 31 2019 *)

Prog

(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-1) for n in (1..30)] # G. C. Greubel, Oct 31 2019

Crossrefs

Cf. A026758, A026759, A026761, A026762, A026763, A026764, A026765, A026766, A026767, A026768.

Sequence in context: A129162 A167660 A290924 * A064914 A243873 A239406

Adjacent sequences: A026757 A026758 A026759 * A026761 A026762 A026763

Keyword

nonn

Author

Clark Kimberling

Status

approved