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 | 0 |
| 4 | 6 |
| 5 | 30 |
| 6 | 180 |
| 7 | 1260 |
| 8 | 8820 |
| 9 | 79380 |
| 10 | 793800 |
| 11 | 8731800 |
| 12 | 106029000 |
| 13 | 1378377000 |
| 14 | 19297278000 |
| 15 | 289459170000 |
| 16 | 4627941318000 |
| 17 | 78675002406000 |
| 18 | 1416150043308000 |
| 19 | 26906850822852000 |
| 20 | 538156815464268000 |