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 | 1 |
| 3 | 0 |
| 4 | -7 |
| 5 | 39 |
| 6 | -139 |
| 7 | 139 |
| 8 | 3249 |
| 9 | -38305 |
| 10 | 257641 |
| 11 | -724681 |
| 12 | -9925519 |
| 13 | 208718223 |
| 14 | -2209932451 |
| 15 | 11619569779 |
| 16 | 98841199521 |
| 17 | -3691083087521 |
| 18 | 56488651405393 |
| 19 | -466578080641297 |
| 20 | -1989509977776479 |
| 21 | 159427986446212959 |
| 22 | -3372599255892634459 |
| 23 | 39809520784433784075 |