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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 22 |
| 5 | 180 |
| 6 | 1902 |
| 7 | 23730 |
| 8 | 344872 |
| 9 | 5706288 |
| 10 | 105960600 |
| 11 | 2181449160 |
| 12 | 49311653616 |
| 13 | 1214109056160 |
| 14 | 32339248301808 |
| 15 | 926527371653520 |
| 16 | 28410493609687680 |
| 17 | 928335829570087680 |
| 18 | 32201658919855225728 |
| 19 | 1181755749910942408320 |
| 20 | 45744743939940787150080 |