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 | -4 |
| 1 | -3 |
| 2 | -4 |
| 3 | -6 |
| 4 | 0 |
| 5 | 120 |
| 6 | 1440 |
| 7 | 15120 |
| 8 | 161280 |
| 9 | 1814400 |
| 10 | 21772800 |
| 11 | 279417600 |
| 12 | 3832012800 |
| 13 | 56043187200 |
| 14 | 871782912000 |
| 15 | 14384418048000 |
| 16 | 251073478656000 |
| 17 | 4623936565248000 |
| 18 | 89633231880192000 |
| 19 | 1824676506132480000 |
| 20 | 38926432130826240000 |
| 21 | 868546016919060480000 |