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 | 3 |
| 4 | -12 |
| 5 | 68 |
| 6 | -480 |
| 7 | 4144 |
| 8 | -42112 |
| 9 | 494360 |
| 10 | -6581880 |
| 11 | 98079696 |
| 12 | -1617373296 |
| 13 | 29245459176 |
| 14 | -575367843960 |
| 15 | 12235339942344 |
| 16 | -279650131845120 |
| 17 | 6836254328079936 |
| 18 | -177979145883651648 |
| 19 | 4916243253642325056 |
| 20 | -143602294106947553280 |
| 21 | 4422411460743707222784 |