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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | 1 |
| 4 | -1 |
| 5 | 1 |
| 6 | -191 |
| 7 | 29 |
| 8 | -2833 |
| 9 | 140051 |
| 10 | -6525613 |
| 11 | 38899057 |
| 12 | -532493977 |
| 13 | 4732769 |
| 14 | -12945933911 |
| 15 | 168070910246641 |
| 16 | -4176262284636781 |
| 17 | 345687837634435 |
| 18 | -26305470121572878741 |
| 19 | 1747464708706073081 |
| 20 | -2811598717039332137041 |
| 21 | 166748874686794522517053 |