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 | 1 |
| 3 | -7 |
| 4 | 49 |
| 5 | -301 |
| 6 | 2281 |
| 7 | -21211 |
| 8 | 260737 |
| 9 | -3254329 |
| 10 | 41086801 |
| 11 | -589336111 |
| 12 | 9851907121 |
| 13 | -170708882917 |
| 14 | 3060177746809 |
| 15 | -60544788499651 |
| 16 | 1298663388032641 |
| 17 | -28777111728560881 |
| 18 | 665551703689032097 |
| 19 | -16413980708818538839 |
| 20 | 428253175770218766001 |