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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | 1 |
| 4 | -5 |
| 5 | 103 |
| 6 | -49 |
| 7 | 2971 |
| 8 | -34409 |
| 9 | 10787 |
| 10 | -567923 |
| 11 | 4857119 |
| 12 | -30312479 |
| 13 | 7045653829 |
| 14 | -77510407993 |
| 15 | 262952596463 |
| 16 | -58196505296117 |
| 17 | 74362625639717 |
| 18 | 172749391066639 |
| 19 | -24672728226124829 |
| 20 | -12265872397466432881 |
| 21 | 1772477431815925044131 |