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 | 1 |
| 3 | 2 |
| 4 | 3 |
| 5 | 12 |
| 6 | 20 |
| 7 | 120 |
| 8 | 315 |
| 9 | 1680 |
| 10 | 6048 |
| 11 | 60480 |
| 12 | 138600 |
| 13 | 1663200 |
| 14 | 9266400 |
| 15 | 69189120 |
| 16 | 340540200 |
| 17 | 5448643200 |
| 18 | 22870848000 |
| 19 | 411675264000 |
| 20 | 2111894104320 |
| 21 | 24135932620800 |
| 22 | 230388447744000 |
| 23 | 5068545850368000 |