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A008325 Number of simple regular trivalent bipartite graphs with 2n nodes. 6
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 (list; graph; refs; listen; history; text; internal format)
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-Fran├žois Alcover, Dec 03 2019 *)

CROSSREFS

Column k=3 of A008327.

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

Sequence in context: A151538 A284998 A009423 * A004066 A123383 A225172

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

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Last modified April 11 12:00 EDT 2021. Contains 342886 sequences. (Running on oeis4.)