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A117421
Column 3 of triangle A117418.
7
1, 4, 14, 50, 191, 780, 3415, 15924, 78595, 408337, 2224365, 12650992, 74876950, 459783611, 2922921341, 19192162340, 129864598566, 903840021981, 6460209847133, 47345351199234, 355305371430875, 2727065598788860
OFFSET
0,2
LINKS
FORMULA
a(n) = A117418(n+3, 3). - G. C. Greubel, May 31 2021
MATHEMATICA
A117418[n_, k_]:= A117418[n, k]= If[k<0 || k>n, 0, If[k==0 || k==n, 1, If[k==n-1, n, Sum[A117418[n -Floor[(k+1)/2], Floor[k/2] +j]*A117418[Floor[(k-1)/2] +j, Floor[(k-1)/2]], {j, 0, n-k}] ]]];
Table[A117418[n+3, 3], {n, 0, 30}] (* G. C. Greubel, May 31 2021 *)
PROG
(Sage)
@CachedFunction
def A117418(n, k):
if (k==0 or k==n): return 1
elif (k==n-1): return n
else: return sum( A117418(n -(k+1)//2, k//2 +j)*A117418((k-1)//2 +j, (k-1)//2) for j in (0..n-k))
[A117418(n+3, 3) for n in (0..30)] # G. C. Greubel, May 31 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Mar 14 2006
STATUS
approved