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 | 4 |
| 3 | 18 |
| 4 | 48 |
| 5 | 1320 |
| 6 | 4200 |
| 7 | 115920 |
| 8 | 994560 |
| 9 | 11793600 |
| 10 | 264055680 |
| 11 | 2601244800 |
| 12 | 67761429120 |
| 13 | 1067726499840 |
| 14 | 21513457405440 |
| 15 | 485310649824000 |
| 16 | 9925206939648000 |
| 17 | 254012624170905600 |
| 18 | 6174538264806912000 |
| 19 | 160933619800835481600 |
| 20 | 4458470291543671603200 |