A005335 - OEIS

%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