A005335 Number of labeled nonseparable (or 2-connected) bipartite graphs with 2n nodes and n nodes in each part.

1, 3, 340, 246295, 796058676, 9736032295374, 432386386904461704, 70004505120317453723895, 41988978212639552393332333300, 95055430627597798399511262461524570, 826275345303020411581696428212189429357784, 27965998400207183955394390590886658323558240477654

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Comments

Nonseparable graphs are also called blocks.

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..50
• F. Harary and R. W. Robinson, Labeled bipartite blocks, Canad. J. Math., 31 (1979), 60-68.
• F. Harary and R. W. Robinson, Labeled bipartite blocks, Canad. J. Math., 31 (1979), 60-68. (Annotated scanned copy)

Crossrefs

Main diagonal of A123474 as an array.

Cf. A005334.

Formula

a(n) = binomial(2*n, n) * A005334(n) / 2. - Andrew Howroyd, Jan 03 2021

Extensions

Name clarified and more terms added by Andrew Howroyd, Jan 03 2021