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 | 3 |
| 4 | -6 |
| 5 | 20 |
| 6 | 0 |
| 7 | -126 |
| 8 | 1260 |
| 9 | -4320 |
| 10 | 5040 |
| 11 | 180180 |
| 12 | -2601720 |
| 13 | 31309200 |
| 14 | -372756384 |
| 15 | 4877195400 |
| 16 | -70178799600 |
| 17 | 1099333347840 |
| 18 | -18429818232960 |
| 19 | 327676010785200 |
| 20 | -6146676161388000 |
| 21 | 121301442091851840 |
| 22 | -2512746856371628800 |
| 23 | 54527094987619716000 |