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
KEYWORD
nonn
AUTHOR
STATUS
approved