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 | -1 |
| 2 | 3 |
| 3 | -8 |
| 4 | 4 |
| 5 | 236 |
| 6 | -3892 |
| 7 | 54552 |
| 8 | -739440 |
| 9 | 9704088 |
| 10 | -116868648 |
| 11 | 1033709040 |
| 12 | 4025264736 |
| 13 | -592337009328 |
| 14 | 23033374965456 |
| 15 | -708140910086400 |
| 16 | 19418661884145024 |
| 17 | -485092601562305664 |
| 18 | 10704418782304457088 |
| 19 | -180835985547961196544 |
| 20 | 431827528992523301376 |
| 21 | 162896031123325288266240 |