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 A129427 Number of isomorphism classes of 3-regular multigraphs of order 2n, loops allowed. 9
 1, 2, 8, 31, 140, 722, 4439, 32654, 289519, 3054067, 37584620, 527968286, 8308434931, 144345554051, 2738280739075, 56245013793246, 1242596591479816, 29366532494796900, 739033832149588904, 19726887762569763453 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS a(1)..a(11) computed using software at http://users.cecs.anu.edu.au/~bdm/nauty/ REFERENCES P. A. Morris, Letter to N. J. A. Sloane, Mar 02 1971. LINKS P. A. Morris, Letter to N. J. A. Sloane, Mar 02 1971. R. C. Read, The enumeration of locally restricted graphs (I), J. London Math. Soc. 34 (1959) 417-436. - Jason Kimberley, Sep 17 2009 FORMULA a(n)=N\{S_{2n}[S_3] * S_{3n}[S_2]\}. - Jason Kimberley, Sep 17 2009 PROG (Sage) h = SymmetricFunctions(ZZ).homogeneous() h([2*n]).plethysm(h([3]).scalar(h([3*n]).plethysm(h([2]))) # Bruce Westbury, Aug 16 2013 CROSSREFS Cf. A005967 (connected, inv. Euler trans.), A129416, A129429, A129431, A129433, A129435, A129437, A005638. Sequence in context: A009567 A150819 A003175 * A150820 A150821 A150822 Adjacent sequences:  A129424 A129425 A129426 * A129428 A129429 A129430 KEYWORD nonn AUTHOR Brendan McKay, Apr 15 2007 EXTENSIONS Using equation (5.8) of Read 1959, new terms a(12) and a(13) were computed in MAGMA by Jason Kimberley, Sep 17 2009 Further terms a(14),a(15),a(16) also computed by Jason Kimberley, announced Nov 09 2009 Formula corrected from n vertices to 2n vertices by Jason Kimberley, Nov 09 2009 Added a(0). - N. J. A. Sloane, Aug 26 2013 a(17)-a(19) from Sean A. Irvine, Oct 29 2016 STATUS approved

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Last modified June 16 13:13 EDT 2019. Contains 324152 sequences. (Running on oeis4.)