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 | 2 |
| 3 | -4 |
| 4 | 9 |
| 5 | -22 |
| 6 | 56 |
| 7 | -148 |
| 8 | 403 |
| 9 | -1123 |
| 10 | 3190 |
| 11 | -9204 |
| 12 | 26900 |
| 13 | -79473 |
| 14 | 236952 |
| 15 | -712046 |
| 16 | 2154304 |
| 17 | -6556711 |
| 18 | 20060425 |
| 19 | -61661700 |
| 20 | 190326371 |
| 21 | -589671041 |
| 22 | 1833130534 |
| 23 | -5716318998 |
| 24 | 17875708018 |
| 25 | -56044448728 |
| 26 | 176130887793 |
| 27 | -554744916727 |
| 28 | 1750798162859 |
| 29 | -5536066777444 |
| 30 | 17536100715442 |