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 | 2 |
| 3 | -3 |
| 4 | 0 |
| 5 | -10 |
| 6 | 160 |
| 7 | -756 |
| 8 | 2688 |
| 9 | -27504 |
| 10 | 341248 |
| 11 | -3113440 |
| 12 | 29004800 |
| 13 | -365574144 |
| 14 | 5120567296 |
| 15 | -69912541440 |
| 16 | 1009388355584 |
| 17 | -16301637449728 |
| 18 | 281310403362816 |
| 19 | -5030932957138944 |
| 20 | 94747161802047488 |
| 21 | -1897026741117419520 |