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) |
|---|---|
| 2 | 1 |
| 3 | 6 |
| 4 | 42 |
| 5 | 330 |
| 6 | 2970 |
| 7 | 30240 |
| 8 | 345240 |
| 9 | 4377240 |
| 10 | 61122600 |
| 11 | 933055200 |
| 12 | 15470254800 |
| 13 | 277005128400 |
| 14 | 5329454130000 |
| 15 | 109681187616000 |
| 16 | 2404894892400000 |
| 17 | 55977698400624000 |
| 18 | 1378748676601296000 |
| 19 | 35829233832135744000 |
| 20 | 979763376201049440000 |
| 21 | 28124715476056399200000 |