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 | -1 |
| 4 | 0 |
| 5 | -15 |
| 6 | 10 |
| 7 | -495 |
| 8 | 840 |
| 9 | -29575 |
| 10 | 87750 |
| 11 | -2805075 |
| 12 | 12340900 |
| 13 | -387547875 |
| 14 | 2304422250 |
| 15 | -73485787375 |
| 16 | 556725078000 |
| 17 | -18311017515375 |
| 18 | 169707184396750 |
| 19 | -5801182757296875 |
| 20 | 63859173696337500 |