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 | 6 |
| 3 | 4 |
| 4 | 15 |
| 5 | 72 |
| 6 | 266 |
| 7 | 1044 |
| 8 | 3780 |
| 9 | 14056 |
| 10 | 51132 |
| 11 | 188604 |
| 12 | 693845 |
| 13 | 2572920 |
| 14 | 9566046 |
| 15 | 35758628 |
| 16 | 134134080 |
| 17 | 505159200 |
| 18 | 1908539864 |
| 19 | 7233104844 |
| 20 | 27486455049 |
| 21 | 104713295712 |
| 22 | 399817073946 |
| 23 | 1529746919604 |