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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | -531440 |
| 4 | 1 |
| 5 | 244140626 |
| 6 | -531440 |
| 7 | -13841287200 |
| 8 | 1 |
| 9 | 282429005041 |
| 10 | 244140626 |
| 11 | -3138428376720 |
| 12 | -531440 |
| 13 | 23298085122482 |
| 14 | -13841287200 |
| 15 | -129746094281440 |
| 16 | 1 |
| 17 | 582622237229762 |
| 18 | 282429005041 |
| 19 | -2213314919066160 |
| 20 | 244140626 |
| 21 | 7355813669568000 |