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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.

A056877 Number of polyominoes with n cells, symmetric about two orthogonal axes.

Table of values

n a(n)
1 0
2 1
3 1
4 1
5 1
6 2
7 3
8 4
9 4
10 8
11 10
12 15
13 17
14 30
15 35
16 60
17 64
18 117
19 128
20 236
21 241
22 459
23 476
24 937
25 912
26 1813
27 1789
28 3706
29 3456
30 7187
31 6779
32 14712
33 13161
34 28571
35 25839
36 58457
37 50348
38 113798
39 98957
40 232718
41 193375
42 453969
43 380522
44 927601
45 745248
46 1813219
47 1468202
48 3702063

List of values

[0, 1, 1, 1, 1, 2, 3, 4, 4, 8, 10, 15, 17, 30, 35, 60, 64, 117, 128, 236, 241, 459, 476, 937, 912, 1813, 1789, 3706, 3456, 7187, 6779, 14712, 13161, 28571, 25839, 58457, 50348, 113798, 98957, 232718, 193375, 453969, 380522, 927601, 745248, 1813219, 1468202, 3702063]

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

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