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 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 3 |
| 4 | 12 |
| 5 | 60 |
| 6 | 420 |
| 7 | 3255 |
| 8 | 28056 |
| 9 | 270144 |
| 10 | 2868840 |
| 11 | 33293205 |
| 12 | 419329020 |
| 13 | 5697423732 |
| 14 | 83069039508 |
| 15 | 1293734268645 |
| 16 | 21436030749840 |
| 17 | 376516868504160 |
| 18 | 6988441065717744 |
| 19 | 136675039085498691 |
| 20 | 2809247116432575420 |
| 21 | 60543293881318183740 |
| 22 | 1365186080156105513460 |