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 | 84 |
| 5 | 660 |
| 6 | 4680 |
| 7 | 47880 |
| 8 | 463680 |
| 9 | 5261760 |
| 10 | 59875200 |
| 11 | 858211200 |
| 12 | 11256537600 |
| 13 | 183697113600 |
| 14 | 2833294464000 |
| 15 | 47730114432000 |
| 16 | 847372990464000 |
| 17 | 17250840262656000 |
| 18 | 329722245844992000 |
| 19 | 7359528574734336000 |
| 20 | 156922179527393280000 |
| 21 | 3601911423105515520000 |
| 22 | 84862054947209379840000 |