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 | 4 |
| 2 | -5 |
| 3 | 10 |
| 4 | -20 |
| 5 | 40 |
| 6 | -80 |
| 7 | 160 |
| 8 | -320 |
| 9 | 640 |
| 10 | -1280 |
| 11 | 2560 |
| 12 | -5120 |
| 13 | 10240 |
| 14 | -20480 |
| 15 | 40960 |
| 16 | -81920 |
| 17 | 163840 |
| 18 | -327680 |
| 19 | 655360 |
| 20 | -1310720 |
| 21 | 2621440 |
| 22 | -5242880 |
| 23 | 10485760 |
| 24 | -20971520 |
| 25 | 41943040 |
| 26 | -83886080 |
| 27 | 167772160 |
| 28 | -335544320 |
| 29 | 671088640 |
| 30 | -1342177280 |
| 31 | 2684354560 |
| 32 | -5368709120 |