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 | 5 |
| 4 | -26 |
| 5 | 204 |
| 6 | -1434 |
| 7 | 16862 |
| 8 | -166536 |
| 9 | 2377512 |
| 10 | -29870400 |
| 11 | 558727872 |
| 12 | -8542202976 |
| 13 | 185546362416 |
| 14 | -3332732184768 |
| 15 | 82441247589360 |
| 16 | -1824937537167744 |
| 17 | 50908186083448320 |
| 18 | -1214743725939310848 |
| 19 | 38998680958184088960 |
| 20 | -1084067907183602910720 |
| 21 | 36452994894649858339584 |