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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | 1 |
| 4 | 0 |
| 5 | -10 |
| 6 | 90 |
| 7 | -730 |
| 8 | 6160 |
| 9 | -55900 |
| 10 | 549900 |
| 11 | -5864300 |
| 12 | 67610400 |
| 13 | -839594600 |
| 14 | 11186357000 |
| 15 | -159300557000 |
| 16 | 2416003824000 |
| 17 | -38894192662000 |
| 18 | 662595375078000 |
| 19 | -11911522255750000 |
| 20 | 225382826562400000 |