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 | 0 |
| 2 | 2 |
| 3 | -6 |
| 4 | 30 |
| 5 | -160 |
| 6 | 1084 |
| 7 | -8316 |
| 8 | 74456 |
| 9 | -749184 |
| 10 | 8474240 |
| 11 | -106035424 |
| 12 | 1459781056 |
| 13 | -21914009728 |
| 14 | 356711937152 |
| 15 | -6258266154752 |
| 16 | 117778607150592 |
| 17 | -2366994133647360 |
| 18 | 50601711980789760 |
| 19 | -1146653711692951552 |