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 | 0 |
| 1 | 2 |
| 2 | 48 |
| 3 | 578 |
| 4 | 4672 |
| 5 | 28610 |
| 6 | 142000 |
| 7 | 596610 |
| 8 | 2187520 |
| 9 | 7159170 |
| 10 | 21278640 |
| 11 | 58227906 |
| 12 | 148321344 |
| 13 | 354870594 |
| 14 | 803467056 |
| 15 | 1732242690 |
| 16 | 3575055360 |
| 17 | 7094825730 |
| 18 | 13591279920 |
| 19 | 25216532290 |
| 20 | 45443741760 |
| 21 | 79749022402 |