A129433 Number of isomorphism classes of 6-regular multigraphs of order n, loops allowed.

1, 4, 13, 66, 384, 3369, 40365, 675368, 14843787, 412444439, 14024069358, 570883006810, 27368160642418, 1525274952640101, 97766102550401217, 7141331463919539567, 589726897233157151109, 54669618693986578729541, 5653861386413841612952683, 648651469510725736002532451

Offset

1,2

Comments

Initial terms computed using software at http://users.cecs.anu.edu.au/~bdm/nauty/

Links

Table of n, a(n) for n=1..20.

R. C. Read, The enumeration of locally restricted graphs (I), J. London Math. Soc. 34 (1959) 417-436. [From Jason Kimberley, Oct 05 2009]

Formula

a(n) = N\{S_n[S_6] * S_{3n}[S_2]\}. [Equation (5.8) of Read 1959]

Euler transform of A129432. - Andrew Howroyd, Mar 15 2020

Crossrefs

Column k=6 of A167625.

Cf. A129432, A129422, A129427, A129429, A129431, A129435, A129437.

Sequence in context: A340452 A222771 A052415 * A157311 A318600 A309900

Adjacent sequences: A129430 A129431 A129432 * A129434 A129435 A129436

Keyword

nonn

Author

Brendan McKay, Apr 15 2007

Extensions

Using the formula, new terms a(13), Oct 05 2009, and a(14)-a(16), Nov 09 2009, were computed in MAGMA by Jason Kimberley

a(17)-a(20) from Andrew Howroyd, Mar 21 2020

Status

approved