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 | -1 |
| 4 | 0 |
| 5 | 9 |
| 6 | -45 |
| 7 | 279 |
| 8 | -2072 |
| 9 | 17265 |
| 10 | -160065 |
| 11 | 1638031 |
| 12 | -18353544 |
| 13 | 223578809 |
| 14 | -2943054205 |
| 15 | 41639195623 |
| 16 | -630238419600 |
| 17 | 10162622387809 |
| 18 | -173942578536993 |
| 19 | 3149754003442847 |
| 20 | -60163773962649200 |
| 21 | 1208991988527548137 |