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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | 4 |
| 4 | -14 |
| 5 | 80 |
| 6 | -496 |
| 7 | 3904 |
| 8 | -34544 |
| 9 | 354560 |
| 10 | -4055296 |
| 11 | 51733504 |
| 12 | -724212224 |
| 13 | 11070525440 |
| 14 | -183218384896 |
| 15 | 3266330312704 |
| 16 | -62380415842304 |
| 17 | 1270842139934720 |
| 18 | -27507260369207296 |
| 19 | 630424777638805504 |
| 20 | -15250924309151350784 |
| 21 | 388362339077351014400 |
| 22 | -10384039093607251050496 |