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 | 0 |
| 4 | 9 |
| 5 | -28 |
| 6 | 65 |
| 7 | 294 |
| 8 | -2751 |
| 9 | 21496 |
| 10 | -69343 |
| 11 | 143154 |
| 12 | 4340193 |
| 13 | -44055100 |
| 14 | 549236753 |
| 15 | -3053333154 |
| 16 | 25428876417 |
| 17 | 103583035888 |
| 18 | -1719503726527 |
| 19 | 62167764668394 |
| 20 | -580794950152287 |
| 21 | 11376539928963260 |
| 22 | -67379231311376719 |