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 | -25 |
| 3 | 49 |
| 4 | -1 |
| 5 | 529 |
| 6 | -1849 |
| 7 | 289 |
| 8 | -9025 |
| 9 | 58081 |
| 10 | -38809 |
| 11 | 108241 |
| 12 | -1560001 |
| 13 | 2283121 |
| 14 | -525625 |
| 15 | 35796289 |
| 16 | -95863681 |
| 17 | 2666689 |
| 18 | -681575449 |
| 19 | 3261894769 |
| 20 | -1289169025 |
| 21 | 9906021841 |
| 22 | -94109673529 |
| 23 | 99199171681 |
| 24 | -84332740801 |
| 25 | 2327696411041 |
| 26 | -4753075824025 |
| 27 | 46970592529 |
| 28 | -48635546218561 |