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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.

A216678 On an n X n grid, number of ways to draw arrows between adjacent nodes such that each node has one outgoing and one incoming arrow, of which the one is not the opposite of the other (i.e., without 2-loops).

Table of values

n a(n)
1 0
2 2
3 0
4 88
5 0
6 207408
7 0
8 22902801416
9 0
10 112398351350823112
11 0
12 24075116871728596710774372

List of values

[0, 2, 0, 88, 0, 207408, 0, 22902801416, 0, 112398351350823112, 0, 24075116871728596710774372]

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

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