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 | 3 |
| 3 | 3 |
| 4 | -5 |
| 5 | -21 |
| 6 | -21 |
| 7 | 43 |
| 8 | 171 |
| 9 | 171 |
| 10 | -341 |
| 11 | -1365 |
| 12 | -1365 |
| 13 | 2731 |
| 14 | 10923 |
| 15 | 10923 |
| 16 | -21845 |
| 17 | -87381 |
| 18 | -87381 |
| 19 | 174763 |
| 20 | 699051 |
| 21 | 699051 |
| 22 | -1398101 |
| 23 | -5592405 |
| 24 | -5592405 |
| 25 | 11184811 |
| 26 | 44739243 |
| 27 | 44739243 |
| 28 | -89478485 |
| 29 | -357913941 |