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 | 6 |
| 4 | 36 |
| 5 | 210 |
| 6 | 1080 |
| 7 | 5460 |
| 8 | 26964 |
| 9 | 132294 |
| 10 | 645480 |
| 11 | 3142590 |
| 12 | 15277680 |
| 13 | 74222616 |
| 14 | 360445176 |
| 15 | 1750067430 |
| 16 | 8496115740 |
| 17 | 41243946330 |
| 18 | 200209950504 |
| 19 | 971859585804 |
| 20 | 4717557894060 |
| 21 | 22899644483430 |
| 22 | 111157568501760 |