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 | -1 |
| 3 | 8 |
| 4 | 19 |
| 5 | -276 |
| 6 | -1002 |
| 7 | 21216 |
| 8 | 103395 |
| 9 | -2881180 |
| 10 | -17620142 |
| 11 | 609297072 |
| 12 | 4483215086 |
| 13 | -185182296040 |
| 14 | -1592692090420 |
| 15 | 76512069014400 |
| 16 | 753146574607395 |
| 17 | -41256108712556460 |
| 18 | -457383584443526790 |
| 19 | 28138583115102810000 |
| 20 | 346933879489006727610 |
| 21 | -23683708768534714984920 |