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 | 0 |
| 1 | 1 |
| 2 | -2 |
| 3 | 6 |
| 4 | -26 |
| 5 | 180 |
| 6 | -1734 |
| 7 | 23464 |
| 8 | -385160 |
| 9 | 7561308 |
| 10 | -166580820 |
| 11 | 4109707800 |
| 12 | -110972371608 |
| 13 | 3276276647280 |
| 14 | -104668338898200 |
| 15 | 3609072471039840 |
| 16 | -133458102348679680 |
| 17 | 5274992059017870048 |
| 18 | -221831508056339323584 |
| 19 | 9893765935654872310656 |
| 20 | -466361328442205843665920 |