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 | -4 |
| 3 | 18 |
| 4 | -95 |
| 5 | 584 |
| 6 | -4123 |
| 7 | 32969 |
| 8 | -294992 |
| 9 | 2922956 |
| 10 | -31791716 |
| 11 | 376719892 |
| 12 | -4832017320 |
| 13 | 66713229192 |
| 14 | -986611705584 |
| 15 | 15561976320144 |
| 16 | -260804276106624 |
| 17 | 4628322010931328 |
| 18 | -86710491660063744 |
| 19 | 1710290952899283456 |
| 20 | -35427639035553292800 |
| 21 | 768970029545198092800 |