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 | -1 |
| 4 | 6 |
| 5 | -11 |
| 6 | 0 |
| 7 | 83 |
| 8 | -784 |
| 9 | 6921 |
| 10 | -34560 |
| 11 | -60281 |
| 12 | 2821632 |
| 13 | -29132611 |
| 14 | 184690688 |
| 15 | -208438245 |
| 16 | -19939461120 |
| 17 | 427918448785 |
| 18 | -5036475875328 |
| 19 | 22588439158415 |
| 20 | 504121321717760 |
| 21 | -15853957892902395 |
| 22 | 258254373528797184 |