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 | -28 |
| 5 | 141 |
| 6 | -846 |
| 7 | 5923 |
| 8 | -47384 |
| 9 | 426457 |
| 10 | -4264570 |
| 11 | 46910271 |
| 12 | -562923252 |
| 13 | 7318002277 |
| 14 | -102452031878 |
| 15 | 1536780478171 |
| 16 | -24588487650736 |
| 17 | 418004290062513 |
| 18 | -7524077221125234 |
| 19 | 142957467201379447 |
| 20 | -2859149344027588940 |
| 21 | 60042136224579367741 |