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 | 1 |
| 4 | 2 |
| 5 | 6 |
| 6 | 144 |
| 7 | 1200 |
| 8 | 9960 |
| 9 | 89040 |
| 10 | 1231776 |
| 11 | 18325440 |
| 12 | 280100160 |
| 13 | 4415368320 |
| 14 | 78497147520 |
| 15 | 1538731434240 |
| 16 | 32250825734400 |
| 17 | 708789321676800 |
| 18 | 16531867860480000 |
| 19 | 410557135229337600 |
| 20 | 10800330695046144000 |
| 21 | 298418233851795456000 |
| 22 | 8641298765266642944000 |