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 | 0 |
| 5 | 29 |
| 6 | -105 |
| 7 | 139 |
| 8 | -2072 |
| 9 | 31737 |
| 10 | -247545 |
| 11 | 1824151 |
| 12 | -22456104 |
| 13 | 313750293 |
| 14 | -3929185169 |
| 15 | 51584719523 |
| 16 | -793292190480 |
| 17 | 13137192234225 |
| 18 | -221862616530705 |
| 19 | 3947317975733039 |
| 20 | -75492532592047280 |
| 21 | 1522475446731094285 |