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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 6 |
| 5 | 30 |
| 6 | 225 |
| 7 | 1575 |
| 8 | 12180 |
| 9 | 109620 |
| 10 | 1100925 |
| 11 | 12110175 |
| 12 | 145259730 |
| 13 | 1888376490 |
| 14 | 26438216805 |
| 15 | 396573252075 |
| 16 | 6345155817000 |
| 17 | 107867648889000 |
| 18 | 1941617990136825 |
| 19 | 36890741812599675 |
| 20 | 737814829704702750 |