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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.

A051568 Let M(n) (A051755) be the maximal number of queens that can be placed on an n X n chessboard so that each queen attacks exactly two other queens; a(n) is the number of non-equivalent solutions. "Non-equivalent" means none of the a(n) solutions can be mapped onto any other solution by board rotations through 90, 180 or 270 degrees or mirror operations along the two diagonals or center lines.

Table of values

n a(n)
3 4
4 2
5 1
6 1
7 5
8 2
9 15
10 3

List of values

[4, 2, 1, 1, 5, 2, 15, 3]

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

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