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 | 11 |
| 5 | 91 |
| 6 | -391 |
| 7 | -4115 |
| 8 | 27971 |
| 9 | 357331 |
| 10 | -3353731 |
| 11 | -50789375 |
| 12 | 607914581 |
| 13 | 10692083221 |
| 14 | -155442170521 |
| 15 | -3120028100285 |
| 16 | 53341649623091 |
| 17 | 1204301220497011 |
| 18 | -23663734574555011 |
| 19 | -593828627529030095 |
| 20 | 13182525824990398001 |