

A014371


Number of trivalent connected simple graphs with 2n nodes and girth at least 4.


27



1, 0, 0, 1, 2, 6, 22, 110, 792, 7805, 97546, 1435720, 23780814, 432757568, 8542471494, 181492137812, 4127077143862
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OFFSET

0,5


COMMENTS

The null graph on 0 vertices is vacuously connected and 3regular; since it is acyclic, it has infinite girth. [Jason Kimberley, Jan 29 2011]


REFERENCES

CRC Handbook of Combinatorial Designs, 1996, p. 647.


LINKS

Table of n, a(n) for n=0..16.
G. Brinkmann, J. Goedgebeur and B. D. McKay, Generation of Cubic graphs, Discrete Mathematics and Theoretical Computer Science, 13 (2) (2011), 6980. (hal00990486)
House of Graphs, Cubic graphs.
Jason Kimberley, Connected regular graphs with girth at least 4
Jason Kimberley, Index of sequences counting connected kregular simple graphs with girth at least g
M. Meringer, Tables of Regular Graphs.
M. Meringer, Fast generation of regular graphs and construction of cages, J. Graph Theory 30 (2) (1999) 137146.


MATHEMATICA

A[s_Integer] := With[{s6 = StringPadLeft[ToString[s], 6, "0"]}, Cases[ Import["https://oeis.org/A" <> s6 <> "/b" <> s6 <> ".txt", "Table"], {_, _}][[All, 2]]];
A002851 = A@002851;
A006923 = A@006923;
a[n_] := A002851[[n + 1]]  A006923[[n + 1]];
a /@ Range[0, 16] (* JeanFrançois Alcover, Jan 27 2020 *)


CROSSREFS

Contribution from Jason Kimberley, Jun 28 2010 and Jan 29 2011: (Start)
3regular simple graphs with girth at least 4: this sequence (connected), A185234 (disconnected), A185334 (not necessarily connected).
Connected kregular simple graphs with girth at least 4: A186724 (any k), A186714 (triangle); specified degree k: A185114 (k=2), this sequence (k=3), A033886 (k=4), A058275 (k=5), A058276 (k=6), A181153 (k=7), A181154 (k=8), A181170 (k=9).
Connected 3regular simple graphs with girth at least g: A185131 (triangle); chosen g: A002851 (g=3), this sequence (g=4), A014372 (g=5), A014374 (g=6), A014375 (g=7), A014376 (g=8).
Connected 3regular simple graphs with girth exactly g: A198303 (triangle); chosen g: A006923 (g=3), A006924 (g=4), A006925 (g=5), A006926 (g=6), A006927 (g=7). (End)
Sequence in context: A129535 A216720 A290279 * A111280 A095817 A101042
Adjacent sequences: A014368 A014369 A014370 * A014372 A014373 A014374


KEYWORD

nonn,nice,more,hard


AUTHOR

N. J. A. Sloane.


EXTENSIONS

Terms a(14) and a(15) appended, from running Meringer's GENREG for 4.2 and 93.2 processor days at U. Newcastle, by Jason Kimberley on Jun 28 2010.
a(16), from House of Graphs, by Jan Goedgebeur et al., added by Jason Kimberley, Feb 15 2011]


STATUS

approved



