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 | -1 |
| 2 | 2 |
| 3 | -3 |
| 4 | 0 |
| 5 | 30 |
| 6 | -240 |
| 7 | 1470 |
| 8 | -6720 |
| 9 | 12600 |
| 10 | 226800 |
| 11 | -4296600 |
| 12 | 48787200 |
| 13 | -407206800 |
| 14 | 1816214400 |
| 15 | 19347728400 |
| 16 | -691775884800 |
| 17 | 12223324713600 |
| 18 | -155222158291200 |
| 19 | 1206712825718400 |
| 20 | 6182374444646400 |
| 21 | -501335892869011200 |
| 22 | 12800637574960435200 |
| 23 | -226664355546012384000 |
| 24 | 2645964108636142694400 |