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A220897
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Number of closed lambda-terms of size n with at most 3 free de Bruijn indices.
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2
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3, 13, 99, 962, 10732, 131715, 1741813, 24537945, 365779679, 5744911157, 94786034723, 1639198623818, 29658034018852, 560484305049943, 11046637024014049, 226728682400563206, 4839249231632997924, 107262821628220974029, 2465723931357450572707
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OFFSET
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0,1
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LINKS
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FORMULA
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Grygiel and Lescanne give a recurrence.
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MATHEMATICA
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T[0, m_] := m; T[n_, m_] := T[n, m] = T[n-1, m+1] + Sum[T[i, m] T[n-i-1, m], {i, 0, n-1}];
a[n_] := T[n, 3];
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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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