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) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 12 |
| 3 | 60 |
| 4 | 280 |
| 5 | 1260 |
| 6 | 5544 |
| 7 | 24024 |
| 8 | 102960 |
| 9 | 437580 |
| 10 | 1847560 |
| 11 | 7759752 |
| 12 | 32449872 |
| 13 | 135207800 |
| 14 | 561632400 |
| 15 | 2326762800 |
| 16 | 9617286240 |
| 17 | 39671305740 |
| 18 | 163352435400 |
| 19 | 671560012200 |
| 20 | 2756930576400 |
| 21 | 11303415363240 |
| 22 | 46290177201840 |
| 23 | 189368906734800 |
| 24 | 773942488394400 |