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 | 2 |
| 2 | -2 |
| 3 | 6 |
| 4 | -28 |
| 5 | 160 |
| 6 | -936 |
| 7 | 4536 |
| 8 | -20448 |
| 9 | 627264 |
| 10 | -19699200 |
| 11 | 43908480 |
| 12 | 17788273920 |
| 13 | -211715112960 |
| 14 | -41219197125120 |
| 15 | 1301670191808000 |
| 16 | 160057006683033600 |
| 17 | -10037518414724505600 |
| 18 | -1007362871616478003200 |