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 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 3 |
| 6 | 8 |
| 7 | 18 |
| 8 | 70 |
| 9 | 180 |
| 10 | 770 |
| 11 | 2610 |
| 12 | 14570 |
| 13 | 54720 |
| 14 | 330960 |
| 15 | 1562814 |
| 16 | 11946080 |
| 17 | 57126780 |
| 18 | 429542960 |
| 19 | 2465050968 |
| 20 | 22517159760 |