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 | 0 |
| 2 | 1 |
| 3 | -3 |
| 4 | 15 |
| 5 | -80 |
| 6 | 542 |
| 7 | -4158 |
| 8 | 37228 |
| 9 | -374592 |
| 10 | 4237120 |
| 11 | -53017712 |
| 12 | 729890528 |
| 13 | -10957004864 |
| 14 | 178355968576 |
| 15 | -3129133077376 |
| 16 | 58889303575296 |
| 17 | -1183497066823680 |
| 18 | 25300855990394880 |
| 19 | -573326855846475776 |