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A220824
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Number of rooted gene trees with n leaves on the label set [4].
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2
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4, 10, 60, 430, 3396, 28818, 256172, 2357138, 22253672, 214370398, 2098593628, 20817790876, 208801698676, 2113957366698, 21574762692484, 221729081428478, 2292720460828372, 23835381083324608, 248987501825970604, 2612160344953154508, 27510833867426222908
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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A[n_, k_] := A[n, k] = If[n < 2, k n, If[OddQ[n], 0, (# (1 - #)/2)&[A[n/2, k]]] + Sum[A[i, k] A[n - i, k], {i, 1, n/2}]];
T[n_, k_] := Sum[(-1)^i Binomial[k, i] A[n, k - i], {i, 0, k}];
a[n_] := T[n, 5];
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CROSSREFS
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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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