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 | 3 |
| 4 | 3 |
| 5 | 30 |
| 6 | 90 |
| 7 | 315 |
| 8 | 315 |
| 9 | 11340 |
| 10 | 113400 |
| 11 | 1247400 |
| 12 | 3742200 |
| 13 | 48648600 |
| 14 | 170270100 |
| 15 | 638512875 |
| 16 | 638512875 |
| 17 | 86837751000 |
| 18 | 3126159036000 |
| 19 | 118794043368000 |
| 20 | 1187940433680000 |
| 21 | 49893498214560000 |
| 22 | 548828480360160000 |
| 23 | 6311527524141840000 |