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 | 2 |
| 2 | 16 |
| 3 | 120 |
| 4 | 882 |
| 5 | 6468 |
| 6 | 47680 |
| 7 | 354224 |
| 8 | 2652688 |
| 9 | 20008864 |
| 10 | 151853312 |
| 11 | 1158365824 |
| 12 | 8873772392 |
| 13 | 68219456080 |
| 14 | 526025997824 |
| 15 | 4066475337152 |
| 16 | 31505967787522 |
| 17 | 244574907064964 |
| 18 | 1901855959279776 |
| 19 | 14811829930479600 |
| 20 | 115514550050260068 |
| 21 | 901993060739459720 |