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 | 2 |
| 2 | 0 |
| 3 | 24 |
| 4 | 256 |
| 5 | 5280 |
| 6 | 129024 |
| 7 | 3893120 |
| 8 | 138215424 |
| 9 | 5657154048 |
| 10 | 262183321600 |
| 11 | 13572739749888 |
| 12 | 776265384591360 |
| 13 | 48609716407476224 |
| 14 | 3307818108252585984 |
| 15 | 243052603284860928000 |
| 16 | 19179014510218162733056 |
| 17 | 1617564760662882792898560 |
| 18 | 145212699111541646687207424 |