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 | 1 |
| 5 | 199 |
| 6 | -1409 |
| 7 | -4579 |
| 8 | 25985 |
| 9 | 23759 |
| 10 | 13872511 |
| 11 | -129511691 |
| 12 | -1050605951 |
| 13 | 4703204375 |
| 14 | 33833371391 |
| 15 | 6781977225869 |
| 16 | -71864943455999 |
| 17 | -926469142419809 |
| 18 | -2738986440688385 |
| 19 | 11032808190085349 |
| 20 | 16738876153047304961 |
| 21 | -146356319119622810521 |