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 | 2 |
| 4 | -2 |
| 5 | 6 |
| 6 | -12 |
| 7 | 30 |
| 8 | -72 |
| 9 | 182 |
| 10 | -464 |
| 11 | 1206 |
| 12 | -3170 |
| 13 | 8426 |
| 14 | -22596 |
| 15 | 61074 |
| 16 | -166194 |
| 17 | 454950 |
| 18 | -1251984 |
| 19 | 3461574 |
| 20 | -9611190 |
| 21 | 26787378 |
| 22 | -74916660 |
| 23 | 210178458 |
| 24 | -591347988 |
| 25 | 1668172842 |
| 26 | -4717282752 |
| 27 | 13369522250 |
| 28 | -37970114702 |
| 29 | 108045430902 |
| 30 | -308001125516 |