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 | 3 |
| 2 | -6 |
| 3 | 36 |
| 4 | -216 |
| 5 | 1404 |
| 6 | -9648 |
| 7 | 68904 |
| 8 | -506304 |
| 9 | 3802464 |
| 10 | -29055024 |
| 11 | 225142416 |
| 12 | -1764900576 |
| 13 | 13970400480 |
| 14 | -111506362560 |
| 15 | 896391836928 |
| 16 | -7251109424640 |
| 17 | 58978357310592 |
| 18 | -482049643011840 |
| 19 | 3957079727715840 |
| 20 | -32609916223598592 |
| 21 | 269682253882186752 |