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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.

A140789 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 TWO lines of symmetry, 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 rotation. If one wishes to count these as different, then each of these numbers can be multiplied by 2.

Table of values

n a(n)
1 0
2 1
3 8
4 32
5 448
6 2240
7 64512
8 556032
9 33521664
10 553615360
11 68717379584
12 2233380896768
13 562949684985856
14 36310271727239168
15 18446744004990074880
16 2370406613402957905920
17 2417851639194073977323520
18 620178945462269582252179456
19 1267650600228193372699684241408

List of values

[0, 1, 8, 32, 448, 2240, 64512, 556032, 33521664, 553615360, 68717379584, 2233380896768, 562949684985856, 36310271727239168, 18446744004990074880, 2370406613402957905920, 2417851639194073977323520, 620178945462269582252179456, 1267650600228193372699684241408]

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

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