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 | -8 |
| 5 | 24 |
| 6 | -76 |
| 7 | 252 |
| 8 | -854 |
| 9 | 2950 |
| 10 | -10343 |
| 11 | 36706 |
| 12 | -131570 |
| 13 | 475576 |
| 14 | -1731357 |
| 15 | 6342042 |
| 16 | -23356185 |
| 17 | 86421603 |
| 18 | -321111661 |
| 19 | 1197586539 |
| 20 | -4481348585 |
| 21 | 16819759474 |
| 22 | -63302097780 |
| 23 | 238835017492 |
| 24 | -903165412289 |
| 25 | 3422512973645 |
| 26 | -12994514592311 |
| 27 | 49425252955926 |