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) |
|---|---|
| 2 | 1 |
| 3 | 3 |
| 4 | -13 |
| 5 | -10 |
| 6 | 394 |
| 7 | -2016 |
| 8 | -5076 |
| 9 | 170064 |
| 10 | -1155024 |
| 11 | -5005440 |
| 12 | 193724640 |
| 13 | -1656720000 |
| 14 | -10280355840 |
| 15 | 465087087360 |
| 16 | -4804977542400 |
| 17 | -39012996556800 |
| 18 | 2035558551398400 |
| 19 | -24660231399014400 |
| 20 | -248246498826547200 |
| 21 | 14713557956794368000 |