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.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 2 |
| 6 | 4 |
| 7 | 28 |
| 8 | 0 |
| 9 | 20 |
| 10 | 20 |
| 11 | 180 |
| 12 | 520 |
| 13 | 1888 |
| 14 | 6016 |
| 15 | 22480 |
| 16 | 105236 |
| 17 | 433500 |
| 18 | 1933604 |
| 19 | 9687268 |
| 20 | 50998366 |
| 21 | 269523272 |
| 22 | 1507984008 |