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 | 3 |
| 2 | 2 |
| 3 | -1 |
| 4 | -2 |
| 5 | -1 |
| 6 | 2 |
| 7 | 3 |
| 8 | 6 |
| 9 | 3 |
| 10 | 18 |
| 11 | 15 |
| 12 | 270 |
| 13 | 255 |
| 14 | 68850 |
| 15 | 68595 |
| 16 | 4722765750 |
| 17 | 4722697155 |
| 18 | 22304192371256441250 |
| 19 | 22304192366533744095 |
| 20 | 497476997228678085728479670747901918750 |
| 21 | 497476997228678085706175478381368174655 |