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 | 0 |
| 3 | 6 |
| 4 | 36 |
| 5 | 150 |
| 6 | 900 |
| 7 | 9366 |
| 8 | 101556 |
| 9 | 1031190 |
| 10 | 10995300 |
| 11 | 134640726 |
| 12 | 1844184276 |
| 13 | 26656678230 |
| 14 | 400614423300 |
| 15 | 6347263038486 |
| 16 | 106960986110196 |
| 17 | 1905688502565270 |
| 18 | 35546025523227300 |
| 19 | 691014283378745046 |
| 20 | 13999772792477879316 |
| 21 | 295570215436360196310 |