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 | 3 |
| 4 | 18 |
| 5 | 90 |
| 6 | 660 |
| 7 | 4620 |
| 8 | 42000 |
| 9 | 378000 |
| 10 | 4142880 |
| 11 | 45571680 |
| 12 | 586776960 |
| 13 | 7628100480 |
| 14 | 113020427520 |
| 15 | 1695306412800 |
| 16 | 28432576972800 |
| 17 | 483353808537600 |
| 18 | 9056055981772800 |
| 19 | 172065063653683200 |
| 20 | 3562946373482496000 |
| 21 | 74821873843132416000 |
| 22 | 1697172166720622592000 |