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 | 1 |
| 2 | 1 |
| 3 | 7 |
| 4 | 7 |
| 5 | 31 |
| 6 | 31 |
| 7 | 127 |
| 8 | 127 |
| 9 | 511 |
| 10 | 511 |
| 11 | 2047 |
| 12 | 2047 |
| 13 | 8191 |
| 14 | 8191 |
| 15 | 32767 |
| 16 | 32767 |
| 17 | 131071 |
| 18 | 131071 |
| 19 | 524287 |
| 20 | 524287 |
| 21 | 2097151 |
| 22 | 2097151 |
| 23 | 8388607 |
| 24 | 8388607 |
| 25 | 33554431 |
| 26 | 33554431 |
| 27 | 134217727 |
| 28 | 134217727 |
| 29 | 536870911 |
| 30 | 536870911 |