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 | 2 |
| 2 | -12 |
| 3 | 90 |
| 4 | -280 |
| 5 | 1050 |
| 6 | -13860 |
| 7 | 70070 |
| 8 | -48048 |
| 9 | 4594590 |
| 10 | -4618900 |
| 11 | 106696590 |
| 12 | -382444920 |
| 13 | 966735770 |
| 14 | -3123300180 |
| 15 | 97045398450 |
| 16 | -97241449760 |
| 17 | 3409528332210 |
| 18 | -3610088822340 |
| 19 | 9399601637426 |
| 20 | -13492251154200 |