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 A005638 Number of unlabeled trivalent (or cubic) graphs with 2n nodes. (Formerly M1656) 25
 1, 0, 1, 2, 6, 21, 94, 540, 4207, 42110, 516344, 7373924, 118573592, 2103205738, 40634185402, 847871397424, 18987149095005, 454032821688754, 11544329612485981, 310964453836198311, 8845303172513781271 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Because the triangle A051031 is symmetric, a(n) is also the number of (2n-4)-regular graphs on 2n vertices. REFERENCES Brinkmann, G. "Fast Generation of Cubic Graphs." J. Graph Th. 23, 139-149, 1996. R. C. Read and R. J. Wilson, An Atlas of Graphs, Oxford, 1998. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Jason Kimberley, Not-necessarily connected regular graphs R. W. Robinson, Cubic graphs (notes) Robinson, R. W.; Wormald, N. C., Numbers of cubic graphs, J. Graph Theory 7 (1983), no. 4, 463-467. Peter Steinbach, Field Guide to Simple Graphs, Volume 1, Part 17 (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.) Eric Weisstein's World of Mathematics, Cubic Graph FORMULA a(n) = A002851(n) + A165653(n). This sequence is the Euler transformation of A002851. CROSSREFS Cf. A000421. 3-regular simple graphs: A002851 (connected), A165653 (disconnected), this sequence (not necessarily connected). Regular graphs A005176 (any degree), A051031 (triangular array), chosen degrees: A000012 (k=0), A059841 (k=1), A008483 (k=2), this sequence (k=3), A033301 (k=4), A165626 (k=5), A165627 (k=6), A165628 (k=7), A180260 (k=8). Not necessarily connected 3-regular simple graphs with girth *at least* g: this sequence (g=3), A185334 (g=4), A185335 (g=5), A185336 (g=6). Not necessarily connected 3-regular simple graphs with girth *exactly* g: A185133 (g=3), A185134 (g=4), A185135 (g=5), A185136 (g=6). Sequence in context: A214087 A183950 A001928 * A249395 A008988 A061232 Adjacent sequences:  A005635 A005636 A005637 * A005639 A005640 A005641 KEYWORD nonn,nice AUTHOR EXTENSIONS More terms from R. C. Read (rcread(AT)math.uwaterloo.ca). Comment, formulas, and (most) crossrefs by Jason Kimberley, 2009 and 2012 STATUS approved

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Last modified October 20 10:45 EDT 2019. Contains 328257 sequences. (Running on oeis4.)