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 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 48 |
| 5 | 360 |
| 6 | 2880 |
| 7 | 25200 |
| 8 | 241920 |
| 9 | 2903040 |
| 10 | 36288000 |
| 11 | 479001600 |
| 12 | 7185024000 |
| 13 | 112086374400 |
| 14 | 1917922406400 |
| 15 | 35307207936000 |
| 16 | 669529276416000 |
| 17 | 13516122267648000 |
| 18 | 294509190463488000 |
| 19 | 6568835422076928000 |
| 20 | 155705728523304960000 |
| 21 | 3882911605049917440000 |