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 | 19 |
| 4 | 128 |
| 5 | 921 |
| 6 | 8912 |
| 7 | 87109 |
| 8 | 1045200 |
| 9 | 13195681 |
| 10 | 188639312 |
| 11 | 2837096637 |
| 12 | 47976425576 |
| 13 | 837845855185 |
| 14 | 16039578298200 |
| 15 | 321739841159317 |
| 16 | 6911395312352672 |
| 17 | 154749452408120385 |
| 18 | 3696709758990757856 |
| 19 | 91546190261460505453 |
| 20 | 2397650607409036823352 |