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 | 2 |
| 3 | 8 |
| 4 | 40 |
| 5 | 240 |
| 6 | 1920 |
| 7 | 17280 |
| 8 | 172800 |
| 9 | 2073600 |
| 10 | 26956800 |
| 11 | 377395200 |
| 12 | 6038323200 |
| 13 | 102651494400 |
| 14 | 1847726899200 |
| 15 | 36954537984000 |
| 16 | 776045297664000 |
| 17 | 17072996548608000 |
| 18 | 409751917166592000 |
| 19 | 10243797929164800000 |
| 20 | 266338746158284800000 |