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 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 20 |
| 6 | 74 |
| 7 | 300 |
| 8 | 1302 |
| 9 | 5944 |
| 10 | 28266 |
| 11 | 139010 |
| 12 | 703102 |
| 13 | 3641956 |
| 14 | 19255106 |
| 15 | 103630920 |
| 16 | 566522778 |
| 17 | 3140130354 |
| 18 | 17620845976 |
| 19 | 99977635264 |
| 20 | 572935630884 |
| 21 | 3313078283974 |