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 | -8 |
| 4 | 21 |
| 5 | 336 |
| 6 | -1445 |
| 7 | -35328 |
| 8 | 212009 |
| 9 | 7010560 |
| 10 | -54073449 |
| 11 | -2258780160 |
| 12 | 21303275389 |
| 13 | 1076400869376 |
| 14 | -12005345614093 |
| 15 | -712084337721344 |
| 16 | 9169911825026385 |
| 17 | 624667885401341952 |
| 18 | -9122376282532978769 |
| 19 | -701910552416102645760 |
| 20 | 11462725659070874233061 |