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 | 9 |
| 2 | 66 |
| 3 | 434 |
| 4 | 2661 |
| 5 | 15525 |
| 6 | 87240 |
| 7 | 475920 |
| 8 | 2534400 |
| 9 | 13227520 |
| 10 | 67866624 |
| 11 | 343105536 |
| 12 | 1712390144 |
| 13 | 8449622016 |
| 14 | 41273524224 |
| 15 | 199782039552 |
| 16 | 959119884288 |
| 17 | 4570314964992 |
| 18 | 21629992173568 |
| 19 | 101729521631232 |
| 20 | 475697692803072 |
| 21 | 2212565287436288 |
| 22 | 10240198466076672 |
| 23 | 47175439742926848 |