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) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 18 |
| 5 | 130 |
| 6 | 1140 |
| 7 | 11886 |
| 8 | 142408 |
| 9 | 1934640 |
| 10 | 29357100 |
| 11 | 492249340 |
| 12 | 9038206056 |
| 13 | 180352513848 |
| 14 | 3886286296984 |
| 15 | 89937276717120 |
| 16 | 2224716791224320 |
| 17 | 58577968147130176 |
| 18 | 1635780290409117648 |
| 19 | 48286974141713673072 |
| 20 | 1502385897082471446880 |