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) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 9 |
| 5 | 45 |
| 6 | 225 |
| 7 | 1575 |
| 8 | 11024 |
| 9 | 99216 |
| 10 | 891984 |
| 11 | 9811824 |
| 12 | 107544862 |
| 13 | 1398083206 |
| 14 | 18043262766 |
| 15 | 270648941490 |
| 16 | 4013029762464 |
| 17 | 68221505961888 |
| 18 | 1141412702224688 |
| 19 | 21686841342269072 |
| 20 | 403841897925538896 |
| 21 | 8480679856436316816 |
| 22 | 173881330973591388704 |