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 | 2 |
| 4 | 12 |
| 5 | 6 |
| 6 | 30 |
| 7 | 150 |
| 8 | 210 |
| 9 | 210 |
| 10 | 210 |
| 11 | 30030 |
| 12 | 13860 |
| 13 | 60060 |
| 14 | 420420 |
| 15 | 4144140 |
| 16 | 9699690 |
| 17 | 87297210 |
| 18 | 717777060 |
| 19 | 4180566390 |
| 20 | 18846497670 |
| 21 | 26004868890 |