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 | 1 |
| 2 | -2 |
| 3 | 6 |
| 4 | -28 |
| 5 | 260 |
| 6 | -3948 |
| 7 | 71120 |
| 8 | -1392368 |
| 9 | 29971008 |
| 10 | -724981920 |
| 11 | 19800726528 |
| 12 | -603571233120 |
| 13 | 20210951379840 |
| 14 | -734663902256256 |
| 15 | 28785160833254400 |
| 16 | -1210241780559067392 |
| 17 | 54390280325210271744 |
| 18 | -2602745536670709682176 |
| 19 | 132118736078618372579328 |