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 | 1 |
| 2 | 2 |
| 3 | 5 |
| 4 | 24 |
| 5 | 154 |
| 6 | 1280 |
| 7 | 13005 |
| 8 | 156800 |
| 9 | 2189726 |
| 10 | 34793472 |
| 11 | 620169186 |
| 12 | 12259602432 |
| 13 | 266267950740 |
| 14 | 6304157663232 |
| 15 | 161624247752253 |
| 16 | 4461403146190848 |
| 17 | 131936409635518774 |
| 18 | 4161949856324648960 |
| 19 | 139508340802911502422 |
| 20 | 4952126960969786064896 |
| 21 | 185585825504872433198636 |