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 | -1 |
| 3 | 0 |
| 4 | 6 |
| 5 | 34 |
| 6 | 150 |
| 7 | 548 |
| 8 | 1064 |
| 9 | -9620 |
| 10 | -190980 |
| 11 | -2379408 |
| 12 | -26412408 |
| 13 | -281137848 |
| 14 | -2923819080 |
| 15 | -29496805392 |
| 16 | -277842087360 |
| 17 | -2151448802448 |
| 18 | -5085750338064 |
| 19 | 334794720634752 |
| 20 | 11987850975483360 |