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 | 5 |
| 4 | 28 |
| 5 | 180 |
| 6 | 1320 |
| 7 | 10920 |
| 8 | 100800 |
| 9 | 1028160 |
| 10 | 11491200 |
| 11 | 139708800 |
| 12 | 1836172800 |
| 13 | 25945920000 |
| 14 | 392302310400 |
| 15 | 6320426112000 |
| 16 | 108101081088000 |
| 17 | 1956280854528000 |
| 18 | 37347179950080000 |
| 19 | 750144785854464000 |
| 20 | 15813863053148160000 |
| 21 | 349121438173347840000 |