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 | 0 |
| 3 | 20 |
| 4 | 192 |
| 5 | 1568 |
| 6 | 12636 |
| 7 | 114216 |
| 8 | 1022604 |
| 9 | 8640980 |
| 10 | 72406668 |
| 11 | 605996308 |
| 12 | 5065065936 |
| 13 | 42045917448 |
| 14 | 346705312932 |
| 15 | 2848191025876 |
| 16 | 23325323646860 |
| 17 | 190440300054560 |
| 18 | 1550193295412264 |
| 19 | 12585187313440032 |
| 20 | 101937894879304356 |
| 21 | 823951520087842720 |
| 22 | 6646993031822674592 |