This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A220895 #15 May 24 2017 02:34:52
%S A220895 1,3,13,76,542,4493,42131,439031,5020105,62382279,835980065,
%T A220895 12004984120,183754242626,2984264710781,51220227153987,
%U A220895 925859588215096,17571969962025822,349210371834021295,7249185099929421649,156847124089924073770,3530125495029323284404
%N A220895 Number of closed lambda-terms of size n with at most 1 free de Bruijn index.
%H A220895 Vincenzo Librandi, <a href="/A220895/b220895.txt">Table of n, a(n) for n = 0..200</a>
%H A220895 Katarzyna Grygiel and Pierre Lescanne, <a href="http://arxiv.org/abs/1210.2610">Counting and generating lambda-terms</a>, arXiv preprint arXiv:1210.2610 [cs.LO], 2012.
%F A220895 Grygiel and Lescanne give a recurrence.
%t A220895 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 A220895 a[n_] := T[n, 1];
%t A220895 Table[a[n], {n, 0, 14}] (* _Jean-François Alcover_, May 23 2017 *)
%K A220895 nonn
%O A220895 0,2
%A A220895 _N. J. A. Sloane_, Dec 31 2012
%E A220895 More terms from _Alois P. Heinz_, May 23 2017