A026749 a(n) = T(2n,n-1), T given by A026747.

1, 6, 30, 143, 671, 3132, 14601, 68101, 318035, 1487661, 6971222, 32727472, 153926409, 725264305, 3423262180, 16185240446, 76648901377, 363557014067, 1726994886004, 8215502584008, 39135887682617, 186676023857041, 891557875400175

Offset

1,2

Links

G. C. Greubel, Table of n, a(n) for n = 1..500

Maple

A026747 := proc(n, k) option remember;
   if k=0 or k = n then 1;
   elif type(n, 'even') and 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) ;
   end if ;
end proc:
seq(A026747(2*n, n-1), n=1..30); # G. C. Greubel, Oct 29 2019

Mathematica

T[n_, k_]:= T[n, k]= If[k==0 || k==n, 1, If[EvenQ[n] && 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[2n, n-1], {n, 30}] (* G. C. Greubel, Oct 29 2019 *)

Prog

(Sage)
@CachedFunction
def T(n, k):
    if (k==0 or k==n): return 1
    elif (mod(n, 2)==0 and 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, n-1) for n in (1..30)] # G. C. Greubel, Oct 29 2019

Crossrefs

Cf. A026747, A026748, A026750, A026751, A026752, A026753, A026754, A026755, A026756, A026757.

Sequence in context: A199938 A285195 A307321 * A003279 A221397 A082134

Adjacent sequences: A026746 A026747 A026748 * A026750 A026751 A026752

Keyword

nonn

Author

Clark Kimberling

Status

approved