%I A019988
%S A019988 1,2,5,16,55,222,950,4265,19591,91678,434005,2073783,9979772,48315186,
%T A019988 235088794,1148891118,5636168859
%N A019988 Number of ways of embedding a connected graph with n edges in the square 
               lattice.
%H A019988 Ed Pegg, Jr., <a href="http://demonstrations.wolfram.com/PolyformExplorer/
               ">Illustrations of polyforms</a>
%H A019988 M. Keller, <a href="http://www.solitairelaboratory.com/polyenum.html">
               Counting polyforms</a>
%H A019988 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               Polyedge.html">Polyedge</a> [From Eric W. Weisstein (eric(AT)weisstein.com), 
               Apr 24 2009]
%Y A019988 Sequence in context: A149972 A026106 A066642 this_sequence A137732 A057973 
               A102461
%Y A019988 Adjacent sequences: A019985 A019986 A019987 this_sequence A019989 A019990 
               A019991
%K A019988 nonn,nice,hard
%O A019988 1,2
%A A019988 Russ Cox (rsc(AT)swtch.com)
%E A019988 More terms from Brendan Owen (brendan_owen(AT)yahoo.com), Feb 20 2002