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A026528
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a(n) = T(2*n-1, n-1), T given by A026519.
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21
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1, 2, 8, 28, 111, 436, 1763, 7176, 29521, 122182, 508595, 2126312, 8923136, 37563930, 158563368, 670893296, 2844444761, 12081753410, 51400091942, 218990735668, 934228356445, 3990177231742, 17060699906541, 73017457810032, 312785412844736, 1340988707637776, 5753539499846507
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listen;
history;
text;
internal format)
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OFFSET
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1,2
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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, 0, If[k==0 || k==2*n, 1, If[k==1 || k==2*n-1, Floor[(n+1)/2], If[EvenQ[n], T[n-1, k-2] + T[n-1, k], T[n-1, k-1] + T[n-1, k-2] + T[n-1, k] ]]]]; (* T = A026519 *)
a[n_]:= a[n]= Block[{$RecursionLimit = Infinity}, T[2*n-1, n-1] ];
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PROG
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(Sage)
@CachedFunction
if (k<0 or k>2*n): return 0
elif (k==0 or k==2*n): return 1
elif (k==1 or k==2*n-1): return (n+1)//2
elif (n%2==0): return T(n-1, k) + T(n-1, k-2)
else: return T(n-1, k) + T(n-1, k-1) + T(n-1, k-2)
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CROSSREFS
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Cf. A026519, A026520, A026521, A026522, A026523, A026524, A026525, A026526, A026527, A026529, A026530, A026531, A026533, A026534, A027262, A027263, A027264, A027265, A027266.
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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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