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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | -1 |
| 5 | 10 |
| 6 | -85 |
| 7 | 735 |
| 8 | -6699 |
| 9 | 64764 |
| 10 | -662780 |
| 11 | 7139000 |
| 12 | -80273116 |
| 13 | 931853208 |
| 14 | -10990479136 |
| 15 | 128253707400 |
| 16 | -1402525474414 |
| 17 | 12224484229744 |
| 18 | -9767136488568 |
| 19 | -3662083220408136 |
| 20 | 144120068237692294 |
| 21 | -4329792070579951500 |
| 22 | 118808185600297890950 |