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 | -18 |
| 4 | 69 |
| 5 | -168 |
| 6 | 504 |
| 7 | -1578 |
| 8 | 4800 |
| 9 | -14310 |
| 10 | 42396 |
| 11 | -128049 |
| 12 | 385839 |
| 13 | -1154271 |
| 14 | 3458847 |
| 15 | -10386477 |
| 16 | 31173873 |
| 17 | -93490386 |
| 18 | 280426833 |
| 19 | -841384614 |
| 20 | 2524300014 |
| 21 | -7572585150 |
| 22 | 22717270491 |
| 23 | -68152872885 |
| 24 | 204460229394 |
| 25 | -613377236379 |
| 26 | 1840126774737 |
| 27 | -5520391488054 |