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 | -7 |
| 5 | 20 |
| 6 | -58 |
| 7 | 177 |
| 8 | -554 |
| 9 | 1769 |
| 10 | -5739 |
| 11 | 18866 |
| 12 | -62684 |
| 13 | 210146 |
| 14 | -709882 |
| 15 | 2413743 |
| 16 | -8253995 |
| 17 | 28366316 |
| 18 | -97916761 |
| 19 | 339326189 |
| 20 | -1180068800 |
| 21 | 4116957243 |
| 22 | -14404398636 |
| 23 | 50530280752 |
| 24 | -177684095927 |
| 25 | 626181400993 |
| 26 | -2211215950469 |
| 27 | 7823025701314 |
| 28 | -27724997048327 |