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 | 4 |
| 3 | 21 |
| 4 | 128 |
| 5 | 745 |
| 6 | 1440 |
| 7 | -89075 |
| 8 | -3031040 |
| 9 | -76951215 |
| 10 | -1784742400 |
| 11 | -39056351675 |
| 12 | -785147904000 |
| 13 | -12815410658375 |
| 14 | -64977212518400 |
| 15 | 8229576066616125 |
| 16 | 587339977981952000 |
| 17 | 29185361934747006625 |
| 18 | 1256364637107240960000 |
| 19 | 48860370609512175371125 |
| 20 | 1686271331087959982080000 |