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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | -3 |
| 4 | 8 |
| 5 | 25 |
| 6 | -121 |
| 7 | -427 |
| 8 | 3128 |
| 9 | 12465 |
| 10 | -124921 |
| 11 | -555731 |
| 12 | 7158128 |
| 13 | 35135945 |
| 14 | -557749921 |
| 15 | -2990414715 |
| 16 | 56767019408 |
| 17 | 329655706465 |
| 18 | -7316056402321 |
| 19 | -45692713833379 |
| 20 | 1164842760597368 |
| 21 | 7777794952988025 |
| 22 | -224574978081433321 |