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 | 9 |
| 4 | 78 |
| 5 | 750 |
| 6 | 8220 |
| 7 | 102900 |
| 8 | 1463280 |
| 9 | 23451120 |
| 10 | 419942880 |
| 11 | 8331634080 |
| 12 | 181689298560 |
| 13 | 4323472433280 |
| 14 | 111534141438720 |
| 15 | 3101254066310400 |
| 16 | 92468631077222400 |
| 17 | 2943141763622860800 |
| 18 | 99596858633182310400 |
| 19 | 3570677764371119001600 |
| 20 | 135190500045467682816000 |