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A026594
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a(n) = T(2*n-1, n-2), where T is given by A026584.
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17
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1, 2, 13, 42, 225, 802, 4235, 15478, 82425, 304156, 1634435, 6064389, 32819839, 122244344, 665162897, 2484851486, 13577768505, 50841782786, 278745377821, 1045763359942, 5749240499515, 21603797860416, 119040956286133, 447922312642212, 2472886893122590, 9315646385012666, 51514464212546865, 194255376492836212
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OFFSET
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2,2
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LINKS
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FORMULA
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MATHEMATICA
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T[n_, k_]:= T[n, k]= If[k==0 || k==2*n, 1, If[k==1 || k==2*n-1, Floor[n/2], If[EvenQ[n+k], T[n-1, k-2] + T[n-1, k], T[n-1, k-2] + T[n-1, k-1] + T[n-1, k]]]]; (*T=A026584*)
Table[T[2*n-1, n-2], {n, 2, 40}] (* G. C. Greubel, Dec 13 2021 *)
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PROG
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(Sage)
@CachedFunction
if (k==0 or k==2*n): return 1
elif (k==1 or k==2*n-1): return (n//2)
else: return T(n-1, k-2) + T(n-1, k) if ((n+k)%2==0) else T(n-1, k-2) + T(n-1, k-1) + T(n-1, k)
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CROSSREFS
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Cf. A026584, A026585, A026587, A026589, A026590, A026591, A026592, A026593, A026595, A026596, A026597, A026598, A026599, A027282, A027283, A027284, A027285, A027286.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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