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 | 1 |
| 5 | 161 |
| 6 | 31 |
| 7 | -8021 |
| 8 | -14335 |
| 9 | 686881 |
| 10 | 2925631 |
| 11 | -91860229 |
| 12 | -583959551 |
| 13 | 15741408385 |
| 14 | 169511794271 |
| 15 | -3832934048789 |
| 16 | -54596554106879 |
| 17 | 1106568438159809 |
| 18 | 23024933751472255 |
| 19 | -412744343093399429 |
| 20 | -11208399032299519999 |
| 21 | 177909311974519181281 |