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 | -5 |
| 3 | -15 |
| 4 | 165 |
| 5 | 630 |
| 6 | -8151 |
| 7 | -33780 |
| 8 | 474045 |
| 9 | 2052495 |
| 10 | -30206330 |
| 11 | -134392230 |
| 12 | 2040588775 |
| 13 | 9248893360 |
| 14 | -143569282680 |
| 15 | -659546365020 |
| 16 | 10407737293965 |
| 17 | 48303692377425 |
| 18 | -771991701692175 |
| 19 | -3611789245335285 |
| 20 | 58311219888996170 |
| 21 | 274581478640096340 |