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) |
|---|---|
| 2 | 1 |
| 3 | 6 |
| 4 | 36 |
| 5 | 240 |
| 6 | 1800 |
| 7 | 15120 |
| 8 | 141120 |
| 9 | 1451520 |
| 10 | 16329600 |
| 11 | 199584000 |
| 12 | 2634508800 |
| 13 | 37362124800 |
| 14 | 566658892800 |
| 15 | 9153720576000 |
| 16 | 156920924160000 |
| 17 | 2845499424768000 |
| 18 | 54420176498688000 |
| 19 | 1094805903679488000 |
| 20 | 23112569077678080000 |
| 21 | 510909421717094400000 |