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) |
|---|---|
| 2 | 1 |
| 3 | 3 |
| 4 | 12 |
| 5 | 80 |
| 6 | 750 |
| 7 | 9072 |
| 8 | 134456 |
| 9 | 2359296 |
| 10 | 47829690 |
| 11 | 1100000000 |
| 12 | 28295372292 |
| 13 | 804925734912 |
| 14 | 25090245516518 |
| 15 | 850408685629440 |
| 16 | 31139121093750000 |
| 17 | 1224979098644774912 |
| 18 | 51523614927176684274 |
| 19 | 2307351090835290783744 |
| 20 | 109607737155696043718780 |
| 21 | 5505024000000000000000000 |