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 | 3 |
| 2 | -3 |
| 3 | -15 |
| 4 | 45 |
| 5 | 315 |
| 6 | -1575 |
| 7 | -14175 |
| 8 | 99225 |
| 9 | 1091475 |
| 10 | -9823275 |
| 11 | -127702575 |
| 12 | 1404728325 |
| 13 | 21070924875 |
| 14 | -273922023375 |
| 15 | -4656674397375 |
| 16 | 69850115960625 |
| 17 | 1327152203251875 |
| 18 | -22561587455281875 |
| 19 | -473793336560919375 |