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) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 840 |
| 7 | 7560 |
| 8 | 83160 |
| 9 | 1081080 |
| 10 | 18378360 |
| 11 | 349188840 |
| 12 | 8031343320 |
| 13 | 200783583000 |
| 14 | 5822723907000 |
| 15 | 180504441117000 |
| 16 | 6678664321329000 |
| 17 | 273825237174489000 |
| 18 | 11774485198503027000 |
| 19 | 553400804329642269000 |
| 20 | 27116639412152471181000 |
| 21 | 1437181888844080972593000 |