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 | 0 |
| 1 | 1 |
| 2 | -2 |
| 3 | 7 |
| 4 | -20 |
| 5 | 61 |
| 6 | -182 |
| 7 | 547 |
| 8 | -1640 |
| 9 | 4921 |
| 10 | -14762 |
| 11 | 44287 |
| 12 | -132860 |
| 13 | 398581 |
| 14 | -1195742 |
| 15 | 3587227 |
| 16 | -10761680 |
| 17 | 32285041 |
| 18 | -96855122 |
| 19 | 290565367 |
| 20 | -871696100 |
| 21 | 2615088301 |
| 22 | -7845264902 |
| 23 | 23535794707 |
| 24 | -70607384120 |
| 25 | 211822152361 |
| 26 | -635466457082 |
| 27 | 1906399371247 |