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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 10 |
| 5 | 68 |
| 6 | 604 |
| 7 | 6584 |
| 8 | 85048 |
| 9 | 1269680 |
| 10 | 21505552 |
| 11 | 407414816 |
| 12 | 8535396256 |
| 13 | 195927013952 |
| 14 | 4890027052480 |
| 15 | 131842951699328 |
| 16 | 3818743350945664 |
| 17 | 118253903175951104 |
| 18 | 3898687202158805248 |
| 19 | 136339489775029813760 |
| 20 | 5040776996774472673792 |