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 | 4 |
| 3 | 18 |
| 4 | 129 |
| 5 | 1095 |
| 6 | 11880 |
| 7 | 149940 |
| 8 | 2218545 |
| 9 | 37147005 |
| 10 | 699281100 |
| 11 | 14561835750 |
| 12 | 332913128625 |
| 13 | 8280095098275 |
| 14 | 222659485448400 |
| 15 | 6434896997529000 |
| 16 | 198909798356894625 |
| 17 | 6547761582390653625 |
| 18 | 228681849947367316500 |
| 19 | 8445341134525197152250 |
| 20 | 328822530412023653630625 |