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 | 0 |
| 2 | -1 |
| 3 | -1 |
| 4 | 0 |
| 5 | 399 |
| 6 | 28 |
| 7 | 162287 |
| 8 | 61440 |
| 9 | 9546255 |
| 10 | 1038576 |
| 11 | 74062575399 |
| 12 | 16756480 |
| 13 | 83695120256591 |
| 14 | 78356634560 |
| 15 | 35181809198207 |
| 16 | 281470681743360 |
| 17 | 246486713303685957375 |
| 18 | 101559922656192 |
| 19 | 604107995057426434824791 |
| 20 | 1152921479006846976 |