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 | -1 |
| 2 | 0 |
| 3 | 3 |
| 4 | 16 |
| 5 | 85 |
| 6 | 516 |
| 7 | 3619 |
| 8 | 28960 |
| 9 | 260649 |
| 10 | 2606500 |
| 11 | 28671511 |
| 12 | 344058144 |
| 13 | 4472755885 |
| 14 | 62618582404 |
| 15 | 939278736075 |
| 16 | 15028459777216 |
| 17 | 255483816212689 |
| 18 | 4598708691828420 |
| 19 | 87375465144739999 |
| 20 | 1747509302894800000 |
| 21 | 36697695360790800021 |
| 22 | 807349297937397600484 |