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 | 2 |
| 2 | 6 |
| 3 | 30 |
| 4 | 120 |
| 5 | 520 |
| 6 | 2184 |
| 7 | 9282 |
| 8 | 39270 |
| 9 | 166430 |
| 10 | 704880 |
| 11 | 2986128 |
| 12 | 12649104 |
| 13 | 53583010 |
| 14 | 226980390 |
| 15 | 961505790 |
| 16 | 4073001576 |
| 17 | 17253515288 |
| 18 | 73087057560 |
| 19 | 309601753890 |
| 20 | 1311494059590 |
| 21 | 5555578014142 |
| 22 | 23533806080736 |
| 23 | 99690802394400 |
| 24 | 422297015565600 |
| 25 | 1788878864806850 |
| 26 | 7577812474550214 |