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) |
|---|---|
| 2 | 1 |
| 3 | 3 |
| 4 | -1 |
| 5 | 0 |
| 6 | 4 |
| 7 | -28 |
| 8 | 188 |
| 9 | -1368 |
| 10 | 11016 |
| 11 | -98208 |
| 12 | 964512 |
| 13 | -10370880 |
| 14 | 121337280 |
| 15 | -1535880960 |
| 16 | 20924455680 |
| 17 | -305396421120 |
| 18 | 4755302899200 |
| 19 | -78700195123200 |
| 20 | 1379748896870400 |
| 21 | -25546854999859200 |
| 22 | 498194992408780800 |
| 23 | -10207190048993280000 |
| 24 | 219216795045212160000 |