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 | -4 |
| 2 | 4 |
| 3 | 56 |
| 4 | -104 |
| 5 | -2464 |
| 6 | 1696 |
| 7 | 181184 |
| 8 | 462016 |
| 9 | -17069824 |
| 10 | -141580544 |
| 11 | 1593913856 |
| 12 | 33015560704 |
| 13 | -47193585664 |
| 14 | -6973651011584 |
| 15 | -50207289585664 |
| 16 | 1214484253413376 |
| 17 | 25500259291480064 |
| 18 | -72069247145590784 |
| 19 | -8696105637665603584 |
| 20 | -81680899029758541824 |