cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A306827 Isomorphism classes of connected 2-in 2-out digraphs, allowing parallel edges but not loops.

Original entry on oeis.org

1, 2, 5, 13, 59, 285, 1987, 16057, 149430, 1551863, 17747299, 221015026
Offset: 2

Views

Author

Brendan McKay, Mar 12 2019

Keywords

Comments

From R. J. Mathar, Mar 15 2019: (Start)
The multiset transform (graphs with n>=2 nodes and k>=1 components) is
1
2
5 1
13 2
59 8 1
285 23 2
1987 100 8 1
16057 468 27 2
149430 2943 115 8 1
The row sums (Euler transform) are A307180. (End)

Examples

			For n=3, the a(3)=2 solutions consist of two superimposed directed triangles, one with the triangles oriented consistently and the other with the triangles oriented oppositely.

Links

Crossrefs

Cf. A219889 (no multiedges, not necessarily connected), A306892 (loops permitted), A307180 (Euler transf.)
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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