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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | -1 |
| 4 | 1 |
| 5 | -16 |
| 6 | 86 |
| 7 | -526 |
| 8 | 302 |
| 9 | -10424 |
| 10 | 323304 |
| 11 | -2805408 |
| 12 | -6563424 |
| 13 | -374664720 |
| 14 | 5877455520 |
| 15 | 32949033168 |
| 16 | -24011091024 |
| 17 | -16610113920768 |
| 18 | 87369247685760 |
| 19 | -5110200130727808 |
| 20 | -23241729685643136 |
| 21 | 1042965176555775744 |
| 22 | 49535245994720788224 |