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 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 110 |
| 6 | 550 |
| 7 | 2922 |
| 8 | 16242 |
| 9 | 93520 |
| 10 | 553980 |
| 11 | 3359384 |
| 12 | 20777588 |
| 13 | 130696662 |
| 14 | 834244830 |
| 15 | 5393850898 |
| 16 | 35272830054 |
| 17 | 233016356788 |
| 18 | 1553427829684 |
| 19 | 10441803227652 |
| 20 | 70715551631992 |
| 21 | 482201548554776 |
| 22 | 3308810614160224 |
| 23 | 22836540660981088 |
| 24 | 158458108961055864 |