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%I M3177 #20 Jan 04 2021 16:56:56
%S 1,3,340,246295,796058676,9736032295374,432386386904461704,
%T 70004505120317453723895,41988978212639552393332333300,
%U 95055430627597798399511262461524570,826275345303020411581696428212189429357784,27965998400207183955394390590886658323558240477654
%N Number of labeled nonseparable (or 2-connected) bipartite graphs with 2n nodes and n nodes in each part.
%C Nonseparable graphs are also called blocks.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H Andrew Howroyd, <a href="/A005335/b005335.txt">Table of n, a(n) for n = 1..50</a>
%H F. Harary and R. W. Robinson, <a href="http://dx.doi.org/10.4153/CJM-1979-007-3">Labeled bipartite blocks</a>, Canad. J. Math., 31 (1979), 60-68.
%H F. Harary and R. W. Robinson, <a href="/A001832/a001832.pdf">Labeled bipartite blocks</a>, Canad. J. Math., 31 (1979), 60-68. (Annotated scanned copy)
%F a(n) = binomial(2*n, n) * A005334(n) / 2. - _Andrew Howroyd_, Jan 03 2021
%Y Main diagonal of A123474 as an array.
%Y Cf. A005334.
%K nonn
%O 1,2
%A _N. J. A. Sloane_
%E Name clarified and more terms added by _Andrew Howroyd_, Jan 03 2021