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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
OFFSET
1,2
LINKS
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
KEYWORD
nonn
STATUS
approved