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 | 1 |
| 2 | 2 |
| 3 | 10 |
| 4 | 48 |
| 5 | 344 |
| 6 | 2400 |
| 7 | 22128 |
| 8 | 223104 |
| 9 | 2520576 |
| 10 | 30689280 |
| 11 | 415560960 |
| 12 | 6058229760 |
| 13 | 95710187520 |
| 14 | 1602520657920 |
| 15 | 28908021381120 |
| 16 | 554882885222400 |
| 17 | 11182172398387200 |
| 18 | 237581975468113920 |
| 19 | 5324332409912033280 |
| 20 | 125630406117045043200 |