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 | -9 |
| 5 | -69 |
| 6 | 483 |
| 7 | 5355 |
| 8 | -80325 |
| 9 | -2081205 |
| 10 | 64517355 |
| 11 | 2738408715 |
| 12 | -172519749045 |
| 13 | -17158004483445 |
| 14 | 2179066569397515 |
| 15 | 365466952872801675 |
| 16 | -93194072982564427125 |
| 17 | -36694334101466364023925 |
| 18 | 18750804725849312016225675 |