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 | -2 |
| 2 | 9 |
| 3 | -46 |
| 4 | 261 |
| 5 | -1578 |
| 6 | 9969 |
| 7 | -65030 |
| 8 | 434685 |
| 9 | -2961922 |
| 10 | 20497577 |
| 11 | -143673630 |
| 12 | 1017887989 |
| 13 | -7277385306 |
| 14 | 52438781409 |
| 15 | -380442087606 |
| 16 | 2776651758189 |
| 17 | -20372853020466 |
| 18 | 150186005826969 |
| 19 | -1111840965284046 |
| 20 | 8262492144613989 |
| 21 | -61614023992470666 |
| 22 | 460907701311527889 |