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 | -39 |
| 5 | 421 |
| 6 | -5809 |
| 7 | 97609 |
| 8 | -1933455 |
| 9 | 44107881 |
| 10 | -1138752449 |
| 11 | 32820576141 |
| 12 | -1044523471991 |
| 13 | 36379398867085 |
| 14 | -1376300966184689 |
| 15 | 56200996031812241 |
| 16 | -2463713702730471199 |
| 17 | 115400572452587463249 |
| 18 | -5751849729149085927425 |
| 19 | 303954806150664749166101 |