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 | 0 |
| 3 | -3 |
| 4 | 26 |
| 5 | -75 |
| 6 | 324 |
| 7 | -3535 |
| 8 | 30988 |
| 9 | -242025 |
| 10 | 2245820 |
| 11 | -26847381 |
| 12 | 339741984 |
| 13 | -4205748547 |
| 14 | 57094691822 |
| 15 | -883946426805 |
| 16 | 14358210544304 |
| 17 | -239959114870689 |
| 18 | 4286519116236900 |
| 19 | -82194727064059645 |
| 20 | 1650577120959962440 |
| 21 | -34495065863164195611 |