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 | 2 |
| 3 | 0 |
| 4 | 12 |
| 5 | 40 |
| 6 | 210 |
| 7 | 840 |
| 8 | 5208 |
| 9 | 23760 |
| 10 | 148410 |
| 11 | 786720 |
| 12 | 5137440 |
| 13 | 30051528 |
| 14 | 207058488 |
| 15 | 1318599240 |
| 16 | 9540828480 |
| 17 | 65319695136 |
| 18 | 495194683680 |
| 19 | 3608366801040 |
| 20 | 28572937581140 |
| 21 | 219952629498840 |
| 22 | 1813839842408748 |
| 23 | 14663194937503288 |
| 24 | 125593649761912704 |
| 25 | 1061139859894326000 |