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 | 0 |
| 3 | 1 |
| 4 | -4 |
| 5 | 33 |
| 6 | -168 |
| 7 | 1377 |
| 8 | -9504 |
| 9 | 99649 |
| 10 | -930560 |
| 11 | 11796673 |
| 12 | -137207552 |
| 13 | 2017677153 |
| 14 | -28086102016 |
| 15 | 471591223841 |
| 16 | -7659623550976 |
| 17 | 144742585812609 |
| 18 | -2686461109796864 |
| 19 | 56447611418620289 |