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 | 1 |
| 2 | -2 |
| 3 | 12 |
| 4 | -96 |
| 5 | 880 |
| 6 | -8720 |
| 7 | 90752 |
| 8 | -975936 |
| 9 | 10737152 |
| 10 | -120093056 |
| 11 | 1360051456 |
| 12 | -15556087296 |
| 13 | 179424700416 |
| 14 | -2084953411584 |
| 15 | 24393551634432 |
| 16 | -287204585508864 |
| 17 | 3400978267127808 |
| 18 | -40480500900446208 |
| 19 | 484006813958356992 |
| 20 | -5810240353159839744 |
| 21 | 70001749695581061120 |