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 | 1 |
| 1 | -5 |
| 2 | 13 |
| 3 | -27 |
| 4 | 54 |
| 5 | -108 |
| 6 | 216 |
| 7 | -432 |
| 8 | 864 |
| 9 | -1728 |
| 10 | 3456 |
| 11 | -6912 |
| 12 | 13824 |
| 13 | -27648 |
| 14 | 55296 |
| 15 | -110592 |
| 16 | 221184 |
| 17 | -442368 |
| 18 | 884736 |
| 19 | -1769472 |
| 20 | 3538944 |
| 21 | -7077888 |
| 22 | 14155776 |
| 23 | -28311552 |
| 24 | 56623104 |
| 25 | -113246208 |
| 26 | 226492416 |
| 27 | -452984832 |
| 28 | 905969664 |
| 29 | -1811939328 |
| 30 | 3623878656 |