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 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 4 |
| 5 | 10 |
| 6 | 20 |
| 7 | 42 |
| 8 | 84 |
| 9 | 170 |
| 10 | 340 |
| 11 | 682 |
| 12 | 1364 |
| 13 | 2730 |
| 14 | 5460 |
| 15 | 10922 |
| 16 | 21844 |
| 17 | 43690 |
| 18 | 87380 |
| 19 | 174762 |
| 20 | 349524 |
| 21 | 699050 |
| 22 | 1398100 |
| 23 | 2796202 |
| 24 | 5592404 |
| 25 | 11184810 |
| 26 | 22369620 |
| 27 | 44739242 |
| 28 | 89478484 |
| 29 | 178956970 |
| 30 | 357913940 |
| 31 | 715827882 |