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 | 1 |
| 3 | 6 |
| 4 | 72 |
| 5 | 960 |
| 6 | 14257 |
| 7 | 228738 |
| 8 | 3896062 |
| 9 | 69590192 |
| 10 | 1291977768 |
| 11 | 24767357824 |
| 12 | 487787117424 |
| 13 | 9830929279248 |
| 14 | 202119964701201 |
| 15 | 4228355224663002 |
| 16 | 89820746194643154 |
| 17 | 1934075860467190608 |
| 18 | 42153272431384984926 |
| 19 | 928785495190695948612 |
| 20 | 20666589509182675178064 |