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 | -4 |
| 4 | 21 |
| 5 | -96 |
| 6 | 520 |
| 7 | -3795 |
| 8 | 32053 |
| 9 | -284368 |
| 10 | 2763876 |
| 11 | -30648465 |
| 12 | 373339824 |
| 13 | -4833294389 |
| 14 | 67167087793 |
| 15 | -1009753574739 |
| 16 | 16215467043493 |
| 17 | -275361718915824 |
| 18 | 4947532173402532 |
| 19 | -94054153646919213 |
| 20 | 1882793796608183356 |
| 21 | -39528099512321898363 |