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 | 0 |
| 3 | 0 |
| 4 | 24 |
| 5 | 0 |
| 6 | -60 |
| 7 | 7980 |
| 8 | -12992 |
| 9 | -23184 |
| 10 | 10320480 |
| 11 | -54616320 |
| 12 | 160009344 |
| 13 | 33740939232 |
| 14 | -391545030240 |
| 15 | 3173349947040 |
| 16 | 211401523687680 |
| 17 | -4586955333880320 |
| 18 | 66611949275370240 |
| 19 | 2068372502060292864 |
| 20 | -82278329345056212480 |
| 21 | 1885659676128917982720 |