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) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 12 |
| 4 | 66 |
| 5 | 450 |
| 6 | 3690 |
| 7 | 35280 |
| 8 | 385560 |
| 9 | 4740120 |
| 10 | 64751400 |
| 11 | 972972000 |
| 12 | 15949256400 |
| 13 | 283232149200 |
| 14 | 5416632421200 |
| 15 | 110988861984000 |
| 16 | 2425817682288000 |
| 17 | 56333385828720000 |
| 18 | 1385151050307024000 |
| 19 | 35950878932544576000 |
| 20 | 982196278209226080000 |
| 21 | 28175806418228108640000 |