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 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 12 |
| 6 | 48 |
| 7 | 240 |
| 8 | 1440 |
| 9 | 11520 |
| 10 | 115200 |
| 11 | 1382400 |
| 12 | 20736000 |
| 13 | 373248000 |
| 14 | 8211456000 |
| 15 | 221709312000 |
| 16 | 7094697984000 |
| 17 | 269598523392000 |
| 18 | 12401532076032000 |
| 19 | 669682732105728000 |
| 20 | 42859694854766592000 |