

A129429


Number of isomorphism classes of 4regular multigraphs of order n, loops allowed.


9



1, 3, 7, 20, 56, 187, 654, 2705, 12587, 67902, 417065, 2897432, 22382255, 189930004, 1750561160, 17380043136, 184653542135, 2088649831822, 25046462480066, 317295911519901, 4233450347175663, 59329632953577985, 871281036897298464
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OFFSET

1,2


COMMENTS

Initial terms computed using software at http://users.cecs.anu.edu.au/~bdm/nauty/
Equation (5.8) of Read's paper tells us a(n) = N {S_n[S_4] * S_{2n}[S_2]}, where we are working with cycle index polynomials.  Jason Kimberley, Oct 05 2009


LINKS

Table of n, a(n) for n=1..23.
R. C. Read, The enumeration of locally restricted graphs (I), J. London Math. Soc. 34 (1959) 417436.


FORMULA

Euler transform of A085549.  Andrew Howroyd, Mar 15 2020


CROSSREFS

Column k=4 of A167625.
Cf. A085549, A129418, A129427, A129431, A129433, A129435, A129437.
Sequence in context: A058737 A274478 A238124 * A084204 A030238 A132364
Adjacent sequences: A129426 A129427 A129428 * A129430 A129431 A129432


KEYWORD

nonn


AUTHOR

Brendan McKay, Apr 15 2007


EXTENSIONS

Using equation (5.8) of Read's paper, new terms a(17)a(19) were computed in MAGMA by Jason Kimberley, Oct 05 2009
Four more terms a(20)a(23) also computed by Jason Kimberley, Nov 09 2009


STATUS

approved



