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 | 1 |
| 3 | 6 |
| 4 | 48 |
| 5 | 360 |
| 6 | 2880 |
| 7 | 25200 |
| 8 | 262080 |
| 9 | 2903040 |
| 10 | 34473600 |
| 11 | 439084800 |
| 12 | 5987520000 |
| 13 | 87178291200 |
| 14 | 1351263513600 |
| 15 | 22230464256000 |
| 16 | 397533007872000 |
| 17 | 7469435990016000 |
| 18 | 147254595231744000 |
| 19 | 3041127510220800000 |
| 20 | 65688354220769280000 |
| 21 | 1481637322979573760000 |