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 | 0 |
| 2 | 2 |
| 3 | -2 |
| 4 | 8 |
| 5 | -20 |
| 6 | 64 |
| 7 | -200 |
| 8 | 656 |
| 9 | -2184 |
| 10 | 7408 |
| 11 | -25456 |
| 12 | 88480 |
| 13 | -310464 |
| 14 | 1098304 |
| 15 | -3912896 |
| 16 | 14026752 |
| 17 | -50557184 |
| 18 | 183110400 |
| 19 | -666079872 |
| 20 | 2432399104 |
| 21 | -8914099840 |
| 22 | 32772922112 |
| 23 | -120844493056 |
| 24 | 446793362944 |
| 25 | -1656004554752 |