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 | -4 |
| 1 | 5 |
| 2 | -13 |
| 3 | 23 |
| 4 | -49 |
| 5 | 95 |
| 6 | -193 |
| 7 | 383 |
| 8 | -769 |
| 9 | 1535 |
| 10 | -3073 |
| 11 | 6143 |
| 12 | -12289 |
| 13 | 24575 |
| 14 | -49153 |
| 15 | 98303 |
| 16 | -196609 |
| 17 | 393215 |
| 18 | -786433 |
| 19 | 1572863 |
| 20 | -3145729 |
| 21 | 6291455 |
| 22 | -12582913 |
| 23 | 25165823 |
| 24 | -50331649 |
| 25 | 100663295 |
| 26 | -201326593 |
| 27 | 402653183 |
| 28 | -805306369 |
| 29 | 1610612735 |
| 30 | -3221225473 |