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 | 0 |
| 3 | 2 |
| 4 | 2 |
| 5 | 0 |
| 6 | 0 |
| 7 | 44 |
| 8 | 260 |
| 9 | 0 |
| 10 | 0 |
| 11 | 33104 |
| 12 | 203712 |
| 13 | 0 |
| 14 | 0 |
| 15 | 75499696 |
| 16 | 621309008 |
| 17 | 0 |
| 18 | 0 |
| 19 | 492805156768 |
| 20 | 5068810602400 |
| 21 | 0 |
| 22 | 0 |
| 23 | 7346944632542720 |