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A026771 a(n) = T(2n,n-1), T given by A026769. 11
1, 6, 31, 156, 784, 3962, 20173, 103522, 535294, 2787700, 14613710, 77072816, 408737760, 2178631156, 11666175215, 62734622764, 338660977020, 1834690352066, 9971834477972, 54361287536706, 297170702049966, 1628670524735842 (list; graph; refs; listen; history; text; internal format)
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 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, n-1), n=1..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, n-1], {n, 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, n-1) for n in (1..30)] # G. C. Greubel, Nov 01 2019

CROSSREFS

Cf. A026769, A026770, A026772, A026773, A026774, A026775, A026776, A026777, A026778, A026779.

Sequence in context: A026705 A243874 A003463 * A289788 A065096 A077352

Adjacent sequences:  A026768 A026769 A026770 * A026772 A026773 A026774

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified July 9 00:55 EDT 2020. Contains 335537 sequences. (Running on oeis4.)