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 | -3 |
| 4 | 15 |
| 5 | 21 |
| 6 | -441 |
| 7 | 477 |
| 8 | 19935 |
| 9 | -101979 |
| 10 | -1150281 |
| 11 | 14838957 |
| 12 | 60479055 |
| 13 | -2328851979 |
| 14 | 3529587879 |
| 15 | 403992301437 |
| 16 | -3333935426625 |
| 17 | -72778393505979 |
| 18 | 1413503392326039 |
| 19 | 10851976875907917 |
| 20 | -554279405351601105 |
| 21 | 713848745428080021 |