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 | 31 |
| 2 | 127 |
| 3 | 8191 |
| 4 | 524287 |
| 5 | 2147483647 |
| 6 | 2305843009213693951 |