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 | 3 |
| 3 | -7 |
| 4 | 15 |
| 5 | -26 |
| 6 | 15 |
| 7 | 153 |
| 8 | -1049 |
| 9 | 4790 |
| 10 | -18522 |
| 11 | 64481 |
| 12 | -206181 |
| 13 | 606384 |
| 14 | -1615121 |
| 15 | 3715993 |
| 16 | -6289929 |
| 17 | 550850 |
| 18 | 61250694 |
| 19 | -382787092 |
| 20 | 1726745790 |
| 21 | -6691501530 |
| 22 | 23413714107 |
| 23 | -75179994017 |
| 24 | 221304346963 |
| 25 | -586004040651 |
| 26 | 1318720868416 |
| 27 | -2044320913276 |
| 28 | -1137686341077 |
| 29 | 28530838758784 |
| 30 | -165361803129585 |