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 | 1 |
| 2 | -1 |
| 3 | 3 |
| 4 | -6 |
| 5 | 18 |
| 6 | -52 |
| 7 | 156 |
| 8 | -481 |
| 9 | 1512 |
| 10 | -4828 |
| 11 | 15621 |
| 12 | -51081 |
| 13 | 168537 |
| 14 | -560309 |
| 15 | 1874975 |
| 16 | -6309964 |
| 17 | 21341241 |
| 18 | -72497698 |
| 19 | 247247463 |
| 20 | -846187023 |
| 21 | 2905210526 |
| 22 | -10003144986 |
| 23 | 34532780087 |
| 24 | -119499263663 |
| 25 | 414431066955 |
| 26 | -1440182574644 |
| 27 | 5014115406096 |