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 | 0 |
| 3 | -18 |
| 4 | 208 |
| 5 | -2400 |
| 6 | 36504 |
| 7 | -663754 |
| 8 | 13808320 |
| 9 | -324176418 |
| 10 | 8487126400 |
| 11 | -245122390601 |
| 12 | 7741417124880 |
| 13 | -265402847130421 |
| 14 | 9816338228638872 |
| 15 | -389618889514254225 |
| 16 | 16518399076342421248 |
| 17 | -745025763154442071130 |
| 18 | 35619835529954597786208 |
| 19 | -1799459812004380374518790 |
| 20 | 95780758238408017088795600 |