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) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 6 |
| 5 | 45 |
| 6 | 435 |
| 7 | 5250 |
| 8 | 76608 |
| 9 | 1316574 |
| 10 | 26100000 |
| 11 | 587030895 |
| 12 | 14780620800 |
| 13 | 412069511139 |
| 14 | 12604714327296 |
| 15 | 419801484375000 |
| 16 | 15123782440058880 |
| 17 | 586049426860524300 |
| 18 | 24307340986526810112 |
| 19 | 1074495780444130114509 |
| 20 | 50429952000000000000000 |