A005335 Number of labeled nonseparable (or 2-connected) bipartite graphs with 2n nodes and n nodes in each part. (Formerly M3177)

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

Offset

1,2

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)

Formula

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

Crossrefs

Main diagonal of A123474 as an array.

Cf. A005334.

Sequence in context: A157585 A045645 A245190 * A318164 A249799 A234607

Adjacent sequences: A005332 A005333 A005334 * A005336 A005337 A005338

Keyword

nonn

Author

N. J. A. Sloane

Extensions

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

Status

approved