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 | 21 |
| 3 | 165 |
| 4 | 1365 |
| 5 | 11628 |
| 6 | 100947 |
| 7 | 888030 |
| 8 | 7888725 |
| 9 | 70607460 |
| 10 | 635745396 |
| 11 | 5752004349 |
| 12 | 52251400851 |
| 13 | 476260169700 |
| 14 | 4353548972850 |
| 15 | 39895566894540 |
| 16 | 366395202809685 |
| 17 | 3371363686069236 |
| 18 | 31074067324187580 |
| 19 | 286845713747883300 |
| 20 | 2651487106659130740 |
| 21 | 24539426037817994160 |