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 | 3 |
| 2 | 12 |
| 3 | 69 |
| 4 | 504 |
| 5 | 4335 |
| 6 | 43200 |
| 7 | 490161 |
| 8 | 6220032 |
| 9 | 87242427 |
| 10 | 1340305920 |
| 11 | 22375475133 |
| 12 | 403237638144 |
| 13 | 7801208775399 |
| 14 | 161245892161536 |
| 15 | 3545854432602345 |
| 16 | 82653484859228160 |
| 17 | 2035605515838402291 |
| 18 | 52814589875313573888 |
| 19 | 1439814136866851346357 |
| 20 | 41145786213980645621760 |