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A026761
a(n) = T(2n, n-2), T given by A026758.
10
1, 8, 48, 259, 1328, 6622, 32483, 157739, 761128, 3657815, 17534231, 83925062, 401363296, 1918822635, 9173429111, 43866599736, 209853869150, 1004463716937, 4810867131369, 23057388013314, 110588897473219, 530808778620583
OFFSET
2,2
LINKS
MAPLE
T:= proc(n, k) option remember;
if n<0 then 0;
elif k=0 or k = n then 1;
elif type(n, 'odd') and 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-2), n=2..30); # G. C. Greubel, Oct 31 2019
MATHEMATICA
T[n_, k_]:= T[n, k]= If[n<0, 0, If[k==0 || k==n, 1, If[OddQ[n] && 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-2], {n, 2, 30}] (* G. C. Greubel, Oct 31 2019 *)
PROG
(Sage)
@CachedFunction
def T(n, k):
if (n<0): return 0
elif (k==0 or k==n): return 1
elif (mod(n, 2)==1 and 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-2) for n in (2..30)] # G. C. Greubel, Oct 31 2019
KEYWORD
nonn
STATUS
approved