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 | -13 |
| 5 | 71 |
| 6 | -461 |
| 7 | 3447 |
| 8 | -29093 |
| 9 | 273343 |
| 10 | -2829325 |
| 11 | 31998903 |
| 12 | -392743957 |
| 13 | 5201061455 |
| 14 | -73943424413 |
| 15 | 1123596277863 |
| 16 | -18176728317413 |
| 17 | 311951144828863 |
| 18 | -5661698774848621 |
| 19 | 108355864447215063 |
| 20 | -2181096921557783605 |