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 | 2 |
| 4 | 2 |
| 5 | 8 |
| 6 | -40 |
| 7 | 144 |
| 8 | 2448 |
| 9 | -17280 |
| 10 | -71424 |
| 11 | 0 |
| 12 | 1198080 |
| 13 | 0 |
| 14 | -18063360 |
| 15 | 418037760 |
| 16 | -7498137600 |
| 17 | -115688079360 |
| 18 | -587977850880 |
| 19 | 12300343050240 |
| 20 | -540240522117120 |
| 21 | -36548032147292160 |
| 22 | 487948583538524160 |
| 23 | -2339225182084792320 |