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 | 1 |
| 3 | -1 |
| 4 | 1 |
| 5 | -121 |
| 6 | 721 |
| 7 | -2521 |
| 8 | 6721 |
| 9 | -378001 |
| 10 | 5473441 |
| 11 | -39972241 |
| 12 | 199679041 |
| 13 | -7005552841 |
| 14 | 176899522801 |
| 15 | -2186722497961 |
| 16 | 17454339826561 |
| 17 | -459473703430561 |
| 18 | 16503993702423361 |
| 19 | -306140370496394401 |
| 20 | 3555223271216311681 |
| 21 | -80917223353652470681 |