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 | -1 |
| 4 | 13 |
| 5 | 19 |
| 6 | -29 |
| 7 | 251 |
| 8 | 281 |
| 9 | -13033 |
| 10 | 56071 |
| 11 | -28601 |
| 12 | -10136411 |
| 13 | 57321419 |
| 14 | -39757717 |
| 15 | -17223709021 |
| 16 | 139901102641 |
| 17 | -12418205969 |
| 18 | -56710054724849 |
| 19 | 628073178260687 |
| 20 | 380303328920381 |
| 21 | -324513582131326141 |
| 22 | 4616335903275095539 |
| 23 | 5642278545451902859 |