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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 5 |
| 4 | 2 |
| 5 | 34 |
| 6 | 324 |
| 7 | 2988 |
| 8 | 28944 |
| 9 | 300816 |
| 10 | 3371040 |
| 11 | 793440 |
| 12 | 49438080 |
| 13 | 1121696640 |
| 14 | 21930773760 |
| 15 | 416139897600 |
| 16 | 7965912729600 |
| 17 | 156343306291200 |
| 18 | 3169866941337600 |
| 19 | 66629845591142400 |
| 20 | 1454242012231680000 |