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 | 4 |
| 3 | -18 |
| 4 | 66 |
| 5 | -230 |
| 6 | 832 |
| 7 | -3118 |
| 8 | 11764 |
| 9 | -44374 |
| 10 | 168476 |
| 11 | -643974 |
| 12 | 2470506 |
| 13 | -9503946 |
| 14 | 36666736 |
| 15 | -141824034 |
| 16 | 549717490 |
| 17 | -2134650662 |
| 18 | 8303024092 |
| 19 | -32343942934 |
| 20 | 126161860886 |
| 21 | -492703658930 |
| 22 | 1926278860624 |
| 23 | -7538530620746 |
| 24 | 29529208903872 |
| 25 | -115766389203370 |