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 | 0 |
| 4 | 4 |
| 5 | 8 |
| 6 | 20 |
| 7 | 40 |
| 8 | 84 |
| 9 | 168 |
| 10 | 340 |
| 11 | 680 |
| 12 | 1364 |
| 13 | 2728 |
| 14 | 5460 |
| 15 | 10920 |
| 16 | 21844 |
| 17 | 43688 |
| 18 | 87380 |
| 19 | 174760 |
| 20 | 349524 |
| 21 | 699048 |
| 22 | 1398100 |
| 23 | 2796200 |
| 24 | 5592404 |
| 25 | 11184808 |
| 26 | 22369620 |
| 27 | 44739240 |
| 28 | 89478484 |
| 29 | 178956968 |
| 30 | 357913940 |
| 31 | 715827880 |