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A220896 Number of closed lambda-terms of size n with at most 2 free de Bruijn indices.

%I A220896 #10 May 23 2017 05:31:58
%S A220896 2,7,41,312,2784,27917,307943,3690055,47635777,658405747,9695617821,
%T A220896 151488900012,2502346785164,43560247035581,796828655891895,
%U A220896 15277217956632472,306268455537216444,6406216616616309707,139535240869213561821,3159084189417388736206
%N A220896 Number of closed lambda-terms of size n with at most 2 free de Bruijn indices.
%H A220896 Katarzyna Grygiel and Pierre Lescanne, <a href="http://arxiv.org/abs/1210.2610">Counting and generating lambda-terms</a>, arXiv preprint arXiv:1210.2610, 2012
%F A220896 Grygiel and Lescanne give a recurrence.
%t A220896 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}];
%t A220896 a[n_] := T[n, 2];
%t A220896 Table[a[n], {n, 0, 14}] (* _Jean-François Alcover_, May 23 2017 *)
%K A220896 nonn
%O A220896 0,1
%A A220896 _N. J. A. Sloane_, Dec 31 2012
%E A220896 More terms from _Alois P. Heinz_, May 23 2017