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 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 30 |
| 6 | 120 |
| 7 | 1560 |
| 8 | 10920 |
| 9 | 185640 |
| 10 | 2042040 |
| 11 | 181741560 |
| 12 | 1090449360 |
| 13 | 254074700880 |
| 14 | 7368166325520 |
| 15 | 449458145856720 |
| 16 | 21124532855265840 |
| 17 | 33735878969859546480 |
| 18 | 640981700427331383120 |
| 19 | 2679944489486672512824720 |
| 20 | 109877724068953573025813520 |