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 | 3 |
| 3 | -15 |
| 4 | 81 |
| 5 | -585 |
| 6 | 4995 |
| 7 | -46935 |
| 8 | 499905 |
| 9 | -6109425 |
| 10 | 79791075 |
| 11 | -1138096575 |
| 12 | 17774982225 |
| 13 | -294439570425 |
| 14 | 5240530570275 |
| 15 | -100050497922375 |
| 16 | 2002010508122625 |
| 17 | -42495475420022625 |
| 18 | 954152290944727875 |