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 | 0 |
| 3 | 6 |
| 4 | 12 |
| 5 | 40 |
| 6 | 540 |
| 7 | 3528 |
| 8 | 25200 |
| 9 | 263520 |
| 10 | 2741760 |
| 11 | 30048480 |
| 12 | 372794400 |
| 13 | 4971957120 |
| 14 | 70612686144 |
| 15 | 1076056027200 |
| 16 | 17469796780800 |
| 17 | 300562292459520 |
| 18 | 5468568356666880 |
| 19 | 104917700221125120 |
| 20 | 2116572758902425600 |
| 21 | 44794683422986936320 |
| 22 | 992435268252158438400 |