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) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 90 |
| 5 | 720 |
| 6 | 7200 |
| 7 | 79200 |
| 8 | 1029600 |
| 9 | 15444000 |
| 10 | 247104000 |
| 11 | 4447872000 |
| 12 | 88957440000 |
| 13 | 1868106240000 |
| 14 | 42966443520000 |
| 15 | 1074161088000000 |
| 16 | 27928188288000000 |
| 17 | 781989272064000000 |
| 18 | 23459678161920000000 |
| 19 | 727250023019520000000 |
| 20 | 23999250759644160000000 |