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 | -4 |
| 3 | -40 |
| 4 | -80 |
| 5 | 352 |
| 6 | 2624 |
| 7 | 3712 |
| 8 | -32000 |
| 9 | -186880 |
| 10 | -134144 |
| 11 | 2885632 |
| 12 | 13520896 |
| 13 | -1269760 |
| 14 | -256000000 |
| 15 | -966164480 |
| 16 | 1056112640 |
| 17 | 22286827520 |
| 18 | 66722201600 |
| 19 | -162411315200 |
| 20 | -1901125959680 |
| 21 | -4329895362560 |