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 | -2 |
| 3 | 5 |
| 4 | -20 |
| 5 | 109 |
| 6 | -738 |
| 7 | 5991 |
| 8 | -56760 |
| 9 | 614601 |
| 10 | -7486670 |
| 11 | 101330635 |
| 12 | -1508641140 |
| 13 | 24503026989 |
| 14 | -431137315434 |
| 15 | 8169513007215 |
| 16 | -165859346028656 |
| 17 | 3591802533860497 |
| 18 | -82644488286784326 |
| 19 | 2013441061219406739 |
| 20 | -51777972823724776620 |
| 21 | 1401611202556240950645 |
| 22 | -39838169568923591411810 |