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 | 0 |
| 2 | 0 |
| 3 | -6 |
| 4 | -36 |
| 5 | -270 |
| 6 | -1620 |
| 7 | -8526 |
| 8 | -41076 |
| 9 | -549870 |
| 10 | -13520340 |
| 11 | -262959246 |
| 12 | -3587233716 |
| 13 | -22581847470 |
| 14 | 584571618540 |
| 15 | 30096769542834 |
| 16 | 859315925548044 |
| 17 | 18434866643574930 |
| 18 | 285138881159407020 |
| 19 | 2045091797042889714 |
| 20 | -28367019385288799796 |
| 21 | 379914681728984325330 |