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 | 2 |
| 3 | 3 |
| 4 | 20 |
| 5 | 70 |
| 6 | 564 |
| 7 | 3108 |
| 8 | 30624 |
| 9 | 230256 |
| 10 | 2705760 |
| 11 | 25771680 |
| 12 | 352805760 |
| 13 | 4067556480 |
| 14 | 63651813120 |
| 15 | 861371884800 |
| 16 | 15176802816000 |
| 17 | 235775183616000 |
| 18 | 4620563523072000 |
| 19 | 81032645804544000 |
| 20 | 1748700390205440000 |