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 | 3 |
| 1 | 15 |
| 2 | 51 |
| 3 | 255 |
| 4 | 771 |
| 5 | 3855 |
| 6 | 13107 |
| 7 | 65535 |
| 8 | 196611 |
| 9 | 983055 |
| 10 | 3342387 |
| 11 | 16711935 |
| 12 | 50529027 |
| 13 | 252645135 |
| 14 | 858993459 |
| 15 | 4294967295 |
| 16 | 12884901891 |
| 17 | 64424509455 |
| 18 | 219043332147 |
| 19 | 1095216660735 |
| 20 | 3311419785987 |
| 21 | 16557098929935 |
| 22 | 56294136361779 |