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 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 2 |
| 6 | 6 |
| 7 | 22 |
| 8 | 86 |
| 9 | 342 |
| 10 | 1303 |
| 11 | 5024 |
| 12 | 19424 |
| 13 | 75120 |
| 14 | 290416 |
| 15 | 1122160 |
| 16 | 4337009 |
| 17 | 16762634 |
| 18 | 64787534 |
| 19 | 250400910 |
| 20 | 967783566 |
| 21 | 3740437902 |
| 22 | 14456621263 |
| 23 | 55874162432 |
| 24 | 215950971648 |
| 25 | 834640190272 |
| 26 | 3225844698176 |
| 27 | 12467736540480 |