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 | 5 |
| 4 | 20 |
| 5 | 180 |
| 6 | 16143 |
| 7 | 489996795 |
| 8 | 1392195548399980210 |
| 9 | 789204635842035039135545297410259322 |