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 | 0 |
| 3 | 1 |
| 4 | -4 |
| 5 | 25 |
| 6 | -194 |
| 7 | 1813 |
| 8 | -19816 |
| 9 | 248113 |
| 10 | -3502630 |
| 11 | 55052701 |
| 12 | -953576876 |
| 13 | 18048491305 |
| 14 | -370623627178 |
| 15 | 8207063150245 |
| 16 | -194950421191504 |
| 17 | 4944881412682081 |
| 18 | -133394451535683278 |
| 19 | 3813510163227155245 |
| 20 | -115170227064335439700 |
| 21 | 3663942710200202043481 |