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 | 4 |
| 3 | 32 |
| 4 | 252 |
| 5 | 1984 |
| 6 | 15620 |
| 7 | 122976 |
| 8 | 968188 |
| 9 | 7622528 |
| 10 | 60012036 |
| 11 | 472473760 |
| 12 | 3719778044 |
| 13 | 29285750592 |
| 14 | 230566226692 |
| 15 | 1815244062944 |
| 16 | 14291386276860 |
| 17 | 112515846151936 |
| 18 | 885835382938628 |
| 19 | 6974167217357088 |
| 20 | 54907502355918076 |
| 21 | 432285851629987520 |
| 22 | 3403379310683982084 |