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 | 1 |
| 2 | 0 |
| 3 | 3 |
| 4 | 12 |
| 5 | 135 |
| 6 | 1440 |
| 7 | 20895 |
| 8 | 342720 |
| 9 | 6585705 |
| 10 | 142430400 |
| 11 | 3449279295 |
| 12 | 92207808000 |
| 13 | 2699909867655 |
| 14 | 85900402748160 |
| 15 | 2951318065570875 |
| 16 | 108894519775641600 |
| 17 | 4294542443185019025 |
| 18 | 180277244225580902400 |
| 19 | 8025792422657714379675 |
| 20 | 377695544010698833920000 |