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 | 2 |
| 3 | 3 |
| 4 | 6 |
| 5 | 15 |
| 6 | 0 |
| 7 | 315 |
| 8 | 1890 |
| 9 | -82215 |
| 10 | 708750 |
| 11 | 41008275 |
| 12 | -1385549550 |
| 13 | -33403344975 |
| 14 | 3426898600125 |
| 15 | 26529571443375 |
| 16 | -13516476003780750 |
| 17 | 157765729690193625 |
| 18 | 84230651703487038750 |
| 19 | -3280917943856839411125 |
| 20 | -799561865724400084556250 |
| 21 | 62859004972802312944044375 |