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 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 12 |
| 5 | 40 |
| 6 | 1980 |
| 7 | 16128 |
| 8 | 136080 |
| 9 | 4224960 |
| 10 | 70943040 |
| 11 | 1087178400 |
| 12 | 31274100000 |
| 13 | 784834652160 |
| 14 | 18115033128192 |
| 15 | 565994928945600 |
| 16 | 18161466717139200 |
| 17 | 560655551681971200 |
| 18 | 20108422243585658880 |
| 19 | 769928646324249699840 |
| 20 | 29464638272901949824000 |