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 | 6 |
| 4 | 48 |
| 5 | 360 |
| 6 | 2880 |
| 7 | 27720 |
| 8 | 322560 |
| 9 | 4173120 |
| 10 | 58665600 |
| 11 | 911433600 |
| 12 | 15567552000 |
| 13 | 287740252800 |
| 14 | 5710178073600 |
| 15 | 121450256928000 |
| 16 | 2758495490150400 |
| 17 | 66563938106265600 |
| 18 | 1699990278213427200 |
| 19 | 45828946821385728000 |
| 20 | 1300703752243703808000 |