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 | -3 |
| 3 | 11 |
| 4 | 57 |
| 5 | -361 |
| 6 | -2763 |
| 7 | 24611 |
| 8 | 250737 |
| 9 | -2873041 |
| 10 | -36581523 |
| 11 | 512343611 |
| 12 | 7828053417 |
| 13 | -129570724921 |
| 14 | -2309644635483 |
| 15 | 44110959165011 |
| 16 | 898621108880097 |
| 17 | -19450718635716001 |
| 18 | -445777636063460643 |
| 19 | 10784052561125704811 |
| 20 | 274613643571568682777 |