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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | 2 |
| 4 | 0 |
| 5 | -6 |
| 6 | 60 |
| 7 | -540 |
| 8 | 3780 |
| 9 | 12600 |
| 10 | -199080 |
| 11 | 3074400 |
| 12 | -45738000 |
| 13 | 511434000 |
| 14 | -5621616000 |
| 15 | 55394539200 |
| 16 | 960323364000 |
| 17 | -24001273296000 |
| 18 | 498178528848000 |
| 19 | -9994137465312000 |
| 20 | 156104172544320000 |
| 21 | -2076607873660320000 |
| 22 | 18061446353670720000 |
| 23 | 206725394268993600000 |