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 | -2 |
| 5 | 6 |
| 6 | -14 |
| 7 | -20 |
| 8 | 876 |
| 9 | -12572 |
| 10 | 157816 |
| 11 | -1953324 |
| 12 | 24704560 |
| 13 | -323390144 |
| 14 | 4399642248 |
| 15 | -62212681544 |
| 16 | 912281561296 |
| 17 | -13817130664560 |
| 18 | 214872589110016 |
| 19 | -3401627908578992 |
| 20 | 54093656991247776 |
| 21 | -844240783639323104 |