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 | 12 |
| 4 | 84 |
| 5 | 700 |
| 6 | 7140 |
| 7 | 84798 |
| 8 | 1148448 |
| 9 | 17508384 |
| 10 | 296577360 |
| 11 | 5525645400 |
| 12 | 112311096480 |
| 13 | 2473005981576 |
| 14 | 58642262698656 |
| 15 | 1489908226161600 |
| 16 | 40377279733096320 |
| 17 | 1162635170476462080 |
| 18 | 35446505436393782400 |
| 19 | 1140734265246337985856 |
| 20 | 38643098112640927503360 |