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 | -4 |
| 3 | 48 |
| 4 | -624 |
| 5 | 9600 |
| 6 | -175680 |
| 7 | 3790080 |
| 8 | -95235840 |
| 9 | 2752081920 |
| 10 | -90328089600 |
| 11 | 3328103116800 |
| 12 | -136191650918400 |
| 13 | 6131573025177600 |
| 14 | -301213549769932800 |
| 15 | 16030999766605824000 |
| 16 | -918678402394841088000 |
| 17 | 56387623092958789632000 |
| 18 | -3690023220507773140992000 |
| 19 | 256425697620583349354496000 |