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 | -1 |
| 4 | 5 |
| 5 | -26 |
| 6 | 91 |
| 7 | -246 |
| 8 | 597 |
| 9 | -1540 |
| 10 | 4576 |
| 11 | -14521 |
| 12 | 44915 |
| 13 | -132328 |
| 14 | 380290 |
| 15 | -1102076 |
| 16 | 3268437 |
| 17 | -9838428 |
| 18 | 29616364 |
| 19 | -88538500 |
| 20 | 263489380 |
| 21 | -785026110 |
| 22 | 2348923875 |
| 23 | -7053379710 |
| 24 | 21204016275 |
| 25 | -63716916276 |
| 26 | 191394838116 |
| 27 | -575200476046 |
| 28 | 1730575897202 |