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 | 9 |
| 2 | 60 |
| 3 | 350 |
| 4 | 1890 |
| 5 | 9702 |
| 6 | 48048 |
| 7 | 231660 |
| 8 | 1093950 |
| 9 | 5080790 |
| 10 | 23279256 |
| 11 | 105462084 |
| 12 | 473227300 |
| 13 | 2106121500 |
| 14 | 9307051200 |
| 15 | 40873466520 |
| 16 | 178520875830 |
| 17 | 775924068150 |
| 18 | 3357800061000 |
| 19 | 14473885526100 |
| 20 | 62168784497820 |
| 21 | 266168518910580 |