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 | 2 |
| 2 | 2 |
| 3 | 2 |
| 4 | 4 |
| 5 | 20 |
| 6 | 4020 |
| 7 | 23086860 |
| 8 | 13991331508857930 |
| 9 | 6090228896601444631429868134927310 |
| 10 | 9346903779275810940456996749711484938792041307270162838305692061624510 |