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 | 8 |
| 3 | -56 |
| 4 | 385 |
| 5 | -2640 |
| 6 | 18096 |
| 7 | -124033 |
| 8 | 850136 |
| 9 | -5826920 |
| 10 | 39938305 |
| 11 | -273741216 |
| 12 | 1876250208 |
| 13 | -12860010241 |
| 14 | 88143821480 |
| 15 | -604146740120 |
| 16 | 4140883359361 |
| 17 | -28382036775408 |
| 18 | 194533374068496 |
| 19 | -1333351581704065 |
| 20 | 9138927697859960 |