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 | 9 |
| 4 | 48 |
| 5 | 305 |
| 6 | 2400 |
| 7 | 22057 |
| 8 | 230272 |
| 9 | 2708001 |
| 10 | 35412480 |
| 11 | 509177801 |
| 12 | 7986468864 |
| 13 | 135718942801 |
| 14 | 2483729876992 |
| 15 | 48699677975145 |
| 16 | 1018542257111040 |
| 17 | 22634000289407297 |
| 18 | 532557637644976128 |
| 19 | 13226748101381102473 |
| 20 | 345792863300174479360 |
| 21 | 9492229607399841038961 |