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 | 40 |
| 5 | 296 |
| 6 | 1576 |
| 7 | 15352 |
| 8 | 104000 |
| 9 | 1276480 |
| 10 | 10556416 |
| 11 | 156843776 |
| 12 | 1533722752 |
| 13 | 26777626240 |
| 14 | 302395339520 |
| 15 | 6068829396736 |
| 16 | 77740741758976 |
| 17 | 1763457842941952 |
| 18 | 25267740818452480 |
| 19 | 639308368122204160 |
| 20 | 10131932297407840256 |
| 21 | 282891828731667890176 |