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 | 1 |
| 2 | 4 |
| 3 | 24 |
| 4 | 168 |
| 5 | 1560 |
| 6 | 17280 |
| 7 | 221760 |
| 8 | 3265920 |
| 9 | 54069120 |
| 10 | 994291200 |
| 11 | 20118067200 |
| 12 | 444034483200 |
| 13 | 10617070464000 |
| 14 | 273391121203200 |
| 15 | 7542665754624000 |
| 16 | 221969877921792000 |
| 17 | 6940528784437248000 |
| 18 | 229781192298577920000 |
| 19 | 8030036368187817984000 |
| 20 | 295390797322766745600000 |