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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 5 |
| 6 | 30 |
| 7 | 210 |
| 8 | 1715 |
| 9 | 15750 |
| 10 | 160650 |
| 11 | 1801800 |
| 12 | 22043175 |
| 13 | 292116825 |
| 14 | 4168464300 |
| 15 | 63725161500 |
| 16 | 1039028615625 |
| 17 | 17998106626500 |
| 18 | 330068683444500 |
| 19 | 6388785205803000 |
| 20 | 130156170633113625 |
| 21 | 2783924007745505625 |
| 22 | 62375052003905891250 |
| 23 | 1460924768552182683750 |