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 | 3 |
| 4 | 9 |
| 5 | -21 |
| 6 | -129 |
| 7 | 111 |
| 8 | 2577 |
| 9 | 2871 |
| 10 | -57249 |
| 11 | -232101 |
| 12 | 1175769 |
| 13 | 11951523 |
| 14 | -6313761 |
| 15 | -542318841 |
| 16 | -1778088159 |
| 17 | 20647593711 |
| 18 | 187318128447 |
| 19 | -386536525389 |
| 20 | -13793029404759 |
| 21 | -41926398389541 |
| 22 | 783578974052799 |
| 23 | 7433562140085663 |
| 24 | -22263437361406671 |
| 25 | -767083139039850201 |