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A117419
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Column 1 of triangle A117418; also row sums of triangle A117418; also column 0 of the matrix square of triangle A117418.
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7
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1, 2, 4, 9, 23, 66, 209, 724, 2722, 11054, 48221, 224549, 1109099, 5778542, 31599830, 180605495, 1074867618, 6641877098, 42500291654, 280917956734, 1913770121847, 13412187670520, 96528097452230, 712332226596239, 5382561715509704
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OFFSET
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0,2
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LINKS
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FORMULA
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MATHEMATICA
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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}] ]]];
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PROG
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(Sage)
@CachedFunction
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))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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