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 | -18 |
| 5 | 118 |
| 6 | -930 |
| 7 | 8888 |
| 8 | -98504 |
| 9 | 1248784 |
| 10 | -17790480 |
| 11 | 281590032 |
| 12 | -4901447232 |
| 13 | 93064850448 |
| 14 | -1914144990576 |
| 15 | 42396742460928 |
| 16 | -1006101059149440 |
| 17 | 25466710774651776 |
| 18 | -684902462140798848 |
| 19 | 19503187752732408576 |
| 20 | -586221766070655432960 |