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 | 0 |
| 4 | 24 |
| 5 | 60 |
| 6 | 240 |
| 7 | 1260 |
| 8 | 68544 |
| 9 | 604800 |
| 10 | 5508000 |
| 11 | 54885600 |
| 12 | 1877420160 |
| 13 | 32069157120 |
| 14 | 499522645440 |
| 15 | 7832035411200 |
| 16 | 236207887534080 |
| 17 | 5868136834560000 |
| 18 | 133085307920947200 |
| 19 | 2941187195765145600 |
| 20 | 91568561750088652800 |
| 21 | 2857211689810118860800 |