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 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 60 |
| 5 | 380 |
| 6 | 3990 |
| 7 | 37002 |
| 8 | 450296 |
| 9 | 5373720 |
| 10 | 76018410 |
| 11 | 1096730030 |
| 12 | 17814654132 |
| 13 | 299645294676 |
| 14 | 5511836578430 |
| 15 | 105550556136690 |
| 16 | 2171244984679920 |
| 17 | 46545825736022192 |
| 18 | 1059273836225051346 |
| 19 | 25100215228045842390 |
| 20 | 626204775725372971820 |
| 21 | 16239127347086448236460 |