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 | 0 |
| 2 | 2 |
| 3 | 24 |
| 4 | 252 |
| 5 | 2880 |
| 6 | 38280 |
| 7 | 594720 |
| 8 | 10565520 |
| 9 | 209502720 |
| 10 | 4558407840 |
| 11 | 107702179200 |
| 12 | 2744400415680 |
| 13 | 75016089308160 |
| 14 | 2189152249764480 |
| 15 | 67906418407027200 |
| 16 | 2230160988344889600 |
| 17 | 77271779968704921600 |
| 18 | 2815893910009609228800 |
| 19 | 107629691727791474841600 |
| 20 | 4304364116456244429388800 |