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 | -1 |
| 3 | 2 |
| 4 | -5 |
| 5 | 10 |
| 6 | 35 |
| 7 | -910 |
| 8 | 11935 |
| 9 | -134750 |
| 10 | 1376375 |
| 11 | -11761750 |
| 12 | 48923875 |
| 13 | 1209057850 |
| 14 | -48943019125 |
| 15 | 1218200233250 |
| 16 | -25136059573625 |
| 17 | 441933961719250 |
| 18 | -5922915844470625 |
| 19 | 18956805373756250 |
| 20 | 2611377778731596875 |