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 | 1 |
| 3 | 3 |
| 4 | 3 |
| 5 | -1 |
| 6 | -1 |
| 7 | 15 |
| 8 | 31 |
| 9 | -1 |
| 10 | -65 |
| 11 | -1 |
| 12 | 255 |
| 13 | 255 |
| 14 | -513 |
| 15 | -1025 |
| 16 | 1023 |
| 17 | 4095 |
| 18 | -1 |
| 19 | -12289 |
| 20 | -8193 |
| 21 | 32767 |
| 22 | 49151 |
| 23 | -65537 |
| 24 | -196609 |
| 25 | 65535 |
| 26 | 655359 |
| 27 | 262143 |
| 28 | -1835009 |
| 29 | -2097153 |
| 30 | 4194303 |
| 31 | 9437183 |
| 32 | -6291457 |
| 33 | -33554433 |
| 34 | -4194305 |
| 35 | 100663295 |
| 36 | 83886079 |
| 37 | -251658241 |