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) |
|---|---|
| 3 | 1 |
| 4 | 4 |
| 5 | 20 |
| 6 | 90 |
| 7 | 420 |
| 8 | 2016 |
| 9 | 10024 |
| 10 | 51640 |
| 11 | 276980 |
| 12 | 1540440 |
| 13 | 8899176 |
| 14 | 53313624 |
| 15 | 330835960 |
| 16 | 2124646720 |
| 17 | 14102514560 |
| 18 | 96622736256 |
| 19 | 682608577104 |
| 20 | 4966188238080 |
| 21 | 37166169295360 |
| 22 | 285813960789280 |
| 23 | 2256147419689856 |
| 24 | 18263257380872064 |
| 25 | 151466260791609600 |