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 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 0 |
| 4 | 24 |
| 5 | 80 |
| 6 | 504 |
| 7 | 3794 |
| 8 | 31616 |
| 9 | 290970 |
| 10 | 2973600 |
| 11 | 33311520 |
| 12 | 405781344 |
| 13 | 5342413414 |
| 14 | 75612197528 |
| 15 | 1144942063230 |
| 16 | 18471128518656 |
| 17 | 316309310084728 |
| 18 | 5730646943736936 |