A307180 - OEIS

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A307180

Isomorphism classes of 2-in 2-out regular digraphs, allowing parallel edges but not loops.

1

1, 0, 1, 2, 6, 15, 68, 310, 2096, 16554, 152497, 1574652, 17947667, 223013311

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,4

LINKS

Table of n, a(n) for n=0..13.

Richard J. Mathar, 2-regular Digraphs of the Lovelock Lagrangian, arXiv:1903.12477 [math.GM], 2019.

CROSSREFS

Cf. A306827 (connected, inverse Eul. Trans.)

Sequence in context: A216811 A351900 A335751 * A009455 A244443 A346555

Adjacent sequences: A307177 A307178 A307179 * A307181 A307182 A307183

KEYWORD

nonn,hard,more

AUTHOR

R. J. Mathar, Mar 28 2019

STATUS

approved