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 | 2 |
| 2 | 0 |
| 3 | 4 |
| 4 | -4 |
| 5 | 12 |
| 6 | -20 |
| 7 | 44 |
| 8 | -84 |
| 9 | 172 |
| 10 | -340 |
| 11 | 684 |
| 12 | -1364 |
| 13 | 2732 |
| 14 | -5460 |
| 15 | 10924 |
| 16 | -21844 |
| 17 | 43692 |
| 18 | -87380 |
| 19 | 174764 |
| 20 | -349524 |
| 21 | 699052 |
| 22 | -1398100 |
| 23 | 2796204 |
| 24 | -5592404 |
| 25 | 11184812 |
| 26 | -22369620 |
| 27 | 44739244 |
| 28 | -89478484 |
| 29 | 178956972 |
| 30 | -357913940 |
| 31 | 715827884 |
| 32 | -1431655764 |
| 33 | 2863311532 |