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 | 6 |
| 5 | 6 |
| 6 | 30 |
| 7 | 150 |
| 8 | 210 |
| 9 | 210 |
| 10 | 210 |
| 11 | 2310 |
| 12 | 2310 |
| 13 | 30030 |
| 14 | 30030 |
| 15 | 30030 |
| 16 | 30030 |
| 17 | 510510 |
| 18 | 510510 |
| 19 | 9699690 |
| 20 | 9699690 |
| 21 | 9699690 |