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 | 1 |
| 3 | -2 |
| 4 | -3 |
| 5 | 56 |
| 6 | -155 |
| 7 | -2736 |
| 8 | 34489 |
| 9 | 72064 |
| 10 | -6599799 |
| 11 | 53676800 |
| 12 | 1155350581 |
| 13 | -32238425088 |
| 14 | -3604716947 |
| 15 | 14790925735936 |
| 16 | -235482791871375 |
| 17 | -4972572910452736 |
| 18 | 254158358486634001 |
| 19 | -1028499606209101824 |
| 20 | -202204782754527137939 |
| 21 | 5371925138905661440000 |