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 | 21 |
| 4 | -111 |
| 5 | -345 |
| 6 | 14895 |
| 7 | -143955 |
| 8 | -760095 |
| 9 | 49774095 |
| 10 | -699437025 |
| 11 | -5221460475 |
| 12 | 458621111025 |
| 13 | -8457966542025 |
| 14 | -81662774418225 |
| 15 | 8999266227076125 |
| 16 | -205480756062957375 |
| 17 | -2434383666448358625 |
| 18 | 322739182334471277375 |
| 19 | -8786388514658364484875 |