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 | -8 |
| 5 | 24 |
| 6 | -72 |
| 7 | 224 |
| 8 | -720 |
| 9 | 2368 |
| 10 | -7936 |
| 11 | 27008 |
| 12 | -93088 |
| 13 | 324288 |
| 14 | -1140032 |
| 15 | 4039296 |
| 16 | -14409728 |
| 17 | 51713792 |
| 18 | -186577152 |
| 19 | 676334592 |
| 20 | -2462090752 |
| 21 | 8997154816 |
| 22 | -32992079872 |
| 23 | 121362092032 |
| 24 | -447721572864 |
| 25 | 1656081763328 |
| 26 | -6140640246784 |
| 27 | 22820403312640 |