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 | 4 |
| 4 | 21 |
| 5 | 130 |
| 6 | 930 |
| 7 | 7560 |
| 8 | 68880 |
| 9 | 695520 |
| 10 | 7711200 |
| 11 | 93139200 |
| 12 | 1217462400 |
| 13 | 17124307200 |
| 14 | 257902444800 |
| 15 | 4140968832000 |
| 16 | 70614415872000 |
| 17 | 1274546617344000 |
| 18 | 24275666967552000 |
| 19 | 486580401635328000 |
| 20 | 10238462617743360000 |
| 21 | 225651661258383360000 |
| 22 | 5198503365971435520000 |