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 | -5 |
| 4 | -23 |
| 5 | 61 |
| 6 | 961 |
| 7 | -209 |
| 8 | -64175 |
| 9 | -197063 |
| 10 | 6153121 |
| 11 | 48453571 |
| 12 | -775290119 |
| 13 | -12038136395 |
| 14 | 116706067297 |
| 15 | 3475641927031 |
| 16 | -17614393396319 |
| 17 | -1188106176788879 |
| 18 | 782498662651585 |
| 19 | 478042340115562507 |
| 20 | 1987706898622853641 |
| 21 | -223468834844001403859 |