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 | 4 |
| 2 | 4 |
| 3 | 10 |
| 4 | 40 |
| 5 | 990 |
| 6 | 8712 |
| 7 | 1691820 |
| 8 | 69466840 |
| 9 | 6173190532 |
| 10 | 4139897208540 |