A026750 a(n) = T(2n,n-2), T given by A026747.

1, 9, 58, 329, 1753, 9020, 45442, 225860, 1112543, 5446607, 26550968, 129042976, 625860205, 3031021096, 14664729519, 70906318405, 342717456708, 1656208470644, 8003645557573, 38681730323747, 186985728069661, 904119336235884

Offset

2,2

Links

G. C. Greubel, Table of n, a(n) for n = 2..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-2), n=2..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-2], {n, 2, 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-2) for n in (2..30)] # G. C. Greubel, Oct 29 2019

Crossrefs

Cf. A026747, A026748, A026749, A026751, A026752, A026753, A026754, A026755, A026756, A026757.

Sequence in context: A304370 A099624 A018218 * A009034 A026377 A016209

Adjacent sequences: A026747 A026748 A026749 * A026751 A026752 A026753

Keyword

nonn

Author

Clark Kimberling

Status

approved