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 | 5 |
| 3 | -1 |
| 4 | 139 |
| 5 | -1 |
| 6 | 859 |
| 7 | 71 |
| 8 | -9769 |
| 9 | 233 |
| 10 | -6395527 |
| 11 | 145069 |
| 12 | -304991568097 |
| 13 | -95164619917 |
| 14 | 119780081383 |
| 15 | -3046785293 |
| 16 | 4002469707564917 |
| 17 | -102407337854027 |
| 18 | 1286572077762833639 |
| 19 | 219276930957009857 |
| 20 | -20109624681057406222913 |
| 21 | 1651690537394493957719 |