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 | 0 |
| 4 | -12 |
| 5 | 180 |
| 6 | -1080 |
| 7 | 15120 |
| 8 | -45360 |
| 9 | -15120 |
| 10 | 6501600 |
| 11 | 166320000 |
| 12 | -6017457600 |
| 13 | 73297224000 |
| 14 | 724669545600 |
| 15 | -32528399904000 |
| 16 | 169180371360000 |
| 17 | 6794185638240000 |
| 18 | -119705492402496000 |
| 19 | 2601008778880512000 |
| 20 | -119160456995099520000 |