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 | 2 |
| 2 | 5 |
| 3 | 18 |
| 4 | 84 |
| 5 | 480 |
| 6 | 3240 |
| 7 | 25200 |
| 8 | 221760 |
| 9 | 2177280 |
| 10 | 23587200 |
| 11 | 279417600 |
| 12 | 3592512000 |
| 13 | 49816166400 |
| 14 | 741015475200 |
| 15 | 11769069312000 |
| 16 | 198766503936000 |
| 17 | 3556874280960000 |
| 18 | 67224923910144000 |
| 19 | 1338096104497152000 |
| 20 | 27978373094031360000 |
| 21 | 613091306060513280000 |