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 | 6 |
| 4 | -12 |
| 5 | 40 |
| 6 | 180 |
| 7 | -1512 |
| 8 | 11760 |
| 9 | -38880 |
| 10 | 20160 |
| 11 | 2106720 |
| 12 | -22381920 |
| 13 | 173197440 |
| 14 | -703999296 |
| 15 | -1737489600 |
| 16 | 86030380800 |
| 17 | -1149696737280 |
| 18 | 11455162974720 |
| 19 | -89560399541760 |
| 20 | 636617260339200 |
| 21 | -6318191386644480 |
| 22 | 139398889956480000 |
| 23 | -3797936822885990400 |