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 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 0 |
| 4 | 12 |
| 5 | 60 |
| 6 | 570 |
| 7 | 8190 |
| 8 | 134456 |
| 9 | 2408616 |
| 10 | 49307670 |
| 11 | 1159112130 |
| 12 | 30619757652 |
| 13 | 891045909468 |
| 14 | 28244653953698 |
| 15 | 969331283419590 |
| 16 | 35858099428919280 |
| 17 | 1423688804991442896 |
| 18 | 60402176709135347502 |
| 19 | 2726896792761748601226 |
| 20 | 130498364319404393167820 |