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 | -1 |
| 3 | 5 |
| 4 | 17 |
| 5 | -121 |
| 6 | -721 |
| 7 | 6845 |
| 8 | 58337 |
| 9 | -698161 |
| 10 | -7734241 |
| 11 | 111973685 |
| 12 | 1526099057 |
| 13 | -25947503401 |
| 14 | -419784870961 |
| 15 | 8200346492525 |
| 16 | 153563504618177 |
| 17 | -3389281372287841 |
| 18 | -72104198836466881 |
| 19 | 1774459993676715365 |
| 20 | 42270463533824671697 |
| 21 | -1147649139272698443481 |