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 | 25 |
| 5 | -41 |
| 6 | -1769 |
| 7 | 7181 |
| 8 | 74705 |
| 9 | -236305 |
| 10 | -7562609 |
| 11 | -4169771 |
| 12 | 1339186729 |
| 13 | -2144219065 |
| 14 | -174083994265 |
| 15 | -370106105251 |
| 16 | 35885107199521 |
| 17 | 252732128552671 |
| 18 | -10892824509622625 |
| 19 | -56149731134394715 |
| 20 | 2589936417283432121 |
| 21 | 31565855231279227319 |