A008325 Number of simple regular trivalent bipartite graphs with 2n nodes.

1, 1, 2, 6, 14, 41, 157, 725, 4196, 29816, 246644, 2297075, 23503477, 260265023, 3090336300, 39101547971, 524782945991, 7443247863498, 111221983956652, 1746165682538497, 28734206614035245, 494526496354065244, 8883865784392246280, 166286434745252091055, 3237719048384605059117, 65477287940472122129194

Offset

3,3

Comments

Euler transform of A006823. - Peter J. Taylor, Sep 28 2017

Links

Table of n, a(n) for n=3..28.

G. Brinkmann, Fast generation of cubic graphs, Journal of Graph Theory, 23(2):139-149, 1996.

Sean A. Irvine, On the difference between A004066 and A008325

Mathematica

A006823 = Cases[Import["https://oeis.org/A006823/b006823.txt", "Table"], {_, _}][[All, 2]];
etr[f_] := Module[{b}, b[n_] := b[n] = If[n == 0, 1, Sum[Sum[d f[d], {d, Divisors[j]}] b[n - j], {j, 1, n}]/n]; b];
b[n_] := If[n >= 3, A006823[[n - 2]], 0];
a = etr[b];
a /@ Range[3, 16] (* Jean-François Alcover, Dec 03 2019 *)

Crossrefs

Column k=3 of A008327.

Cf. A004066 (bicolored), A006823 (connected).

Sequence in context: A151538 A284998 A009423 * A004066 A123383 A281707

Adjacent sequences: A008322 A008323 A008324 * A008326 A008327 A008328

Keyword

nonn,hard

Author

Brendan McKay

Extensions

a(15)-a(16) from Peter J. Taylor, Sep 28 2017

Terms a(17) and beyond from Andrew Howroyd, Apr 03 2020

Status

approved