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 | 17 |
| 4 | 399 |
| 5 | 7849 |
| 6 | 162287 |
| 7 | 3667649 |
| 8 | 91171007 |
| 9 | 2486784401 |
| 10 | 74062575399 |
| 11 | 2395420006033 |
| 12 | 83695120256591 |
| 13 | 3143661612445145 |
| 14 | 126375169532421599 |
| 15 | 5415486851106043649 |
| 16 | 246486713303685957375 |
| 17 | 11877172892329028459041 |
| 18 | 604107995057426434824791 |