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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.

A133189 Number of simple directed graphs on n labeled nodes consisting only of some cycle graphs C_2 and nodes not part of a cycle having directed edges to both nodes in exactly one cycle.

Table of values

n a(n)
0 1
1 0
2 1
3 3
4 9
5 40
6 210
7 1176
8 7273
9 49932
10 372060
11 2971540
12 25359411
13 230364498
14 2215550428
15 22460391240
16 239236043985
17 2669869110856
18 31134833803728
19 378485082644400
20 4786085290280275
21 62838103267148790
22 855122923978737876
23 12042364529117844328

List of values

[1, 0, 1, 3, 9, 40, 210, 1176, 7273, 49932, 372060, 2971540, 25359411, 230364498, 2215550428, 22460391240, 239236043985, 2669869110856, 31134833803728, 378485082644400, 4786085290280275, 62838103267148790, 855122923978737876, 12042364529117844328]

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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