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) |
|---|---|
| 1 | 1 |
| 2 | -5 |
| 3 | 35 |
| 4 | -275 |
| 5 | 2275 |
| 6 | -19255 |
| 7 | 163925 |
| 8 | -1385725 |
| 9 | 11483875 |
| 10 | -91781375 |
| 11 | 688658785 |
| 12 | -4581861025 |
| 13 | 22550427925 |
| 14 | 8852899375 |
| 15 | -2431720493125 |
| 16 | 47471706909725 |
| 17 | -699843878180125 |
| 18 | 9141002535744625 |
| 19 | -111232778205154375 |
| 20 | 1288777160650004375 |
| 21 | -14372445132730778975 |