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 | -5 |
| 4 | 25 |
| 5 | 161 |
| 6 | -1409 |
| 7 | -12221 |
| 8 | 158705 |
| 9 | 1733185 |
| 10 | -30136769 |
| 11 | -397326709 |
| 12 | 8696945929 |
| 13 | 134416055905 |
| 14 | -3555479651905 |
| 15 | -63044502191789 |
| 16 | 1957884163020001 |
| 17 | 39178556553643649 |
| 18 | -1398250387206450305 |
| 19 | -31169265056007817445 |
| 20 | 1257498026543130033401 |