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 | 1 |
| 2 | 1 |
| 3 | 8 |
| 4 | 30 |
| 5 | 264 |
| 6 | 1920 |
| 7 | 20880 |
| 8 | 226800 |
| 9 | 3064320 |
| 10 | 43908480 |
| 11 | 722131200 |
| 12 | 12773376000 |
| 13 | 249559833600 |
| 14 | 5236924492800 |
| 15 | 118911189196800 |
| 16 | 2883421981440000 |
| 17 | 74715282690048000 |
| 18 | 2054450584682496000 |
| 19 | 59855791774851072000 |
| 20 | 1839882143683584000000 |