A026774 a(n) = T(2n-1,n-2), T given by A026769.

1, 8, 49, 276, 1504, 8082, 43193, 230536, 1231484, 6591350, 35369380, 190329098, 1027180798, 5559635866, 30176648513, 164237973028, 896188159820, 4902187071922, 26877397858264, 147684225578318, 813159429830590

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 n=2 and k=1 then 2;
   elif 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-1, n-2), n=2..30); # G. C. Greubel, Nov 01 2019

Mathematica

T[n_, k_]:= T[n, k]= If[n<0, 0, If[k==0 || k==n, 1, If[n==2 && k==1, 2, If[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-1, n-2], {n, 2, 30}] (* G. C. Greubel, Nov 01 2019 *)

Prog

(Sage)
@CachedFunction
def T(n, k):
    if (k==0 or k==n): return 1
    elif (n==2 and k==1): return 2
    elif (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-1, n-2) for n in (2..30)] # G. C. Greubel, Nov 01 2019

Crossrefs

Cf. A026769, A026770, A026771, A026772, A026773, A026775, A026776, A026777, A026778, A026779.

Sequence in context: A026389 A005059 A026719 * A089383 A351128 A200660

Adjacent sequences: A026771 A026772 A026773 * A026775 A026776 A026777

Keyword

nonn

Author

Clark Kimberling

Status

approved