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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.

A140795 We consider how many ways there are of coloring a square grid, n X n, using just two colors, black & white say. If the resulting grid has rotational symmetry of order two only, then the number of different grids is given by this sequence. None of these counted are the images of any of the others under a reflection or a rotation of 90 degrees. If one wishes to count these as different, then each of these numbers can be multiplied by 4.

Table of values

n a(n)
1 0
2 0
3 2
4 44
5 1792
6 64288
7 8354304
8 1073447424
9 549738528768
10 281474691514368
11 576460717407862784
12 1180591619583540985856
13 9671406556633359531900928
14 79228162514246041720191975424
15 2596148429267404554864448650608640
16 85070591730234614676028659138035712000

List of values

[0, 0, 2, 44, 1792, 64288, 8354304, 1073447424, 549738528768, 281474691514368, 576460717407862784, 1180591619583540985856, 9671406556633359531900928, 79228162514246041720191975424, 2596148429267404554864448650608640, 85070591730234614676028659138035712000]

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

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