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 | -5 |
| 4 | 7 |
| 5 | -15 |
| 6 | 7601 |
| 7 | -91 |
| 8 | 3617 |
| 9 | -745739 |
| 10 | 3317609 |
| 11 | -5981591 |
| 12 | 5436374093 |
| 13 | -213827575 |
| 14 | 213745149261 |
| 15 | -249859397004145 |
| 16 | 238988952277727 |
| 17 | -28354566442037 |
| 18 | 26315271553053477373 |
| 19 | -108409774812137683 |
| 20 | 3394075340453838586663 |