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 | 6 |
| 3 | 42 |
| 4 | 456 |
| 5 | 5640 |
| 6 | 93600 |
| 7 | 1728720 |
| 8 | 38344320 |
| 9 | 948931200 |
| 10 | 26555558400 |
| 11 | 817935148800 |
| 12 | 27735629644800 |
| 13 | 1020596255078400 |
| 14 | 40642432179148800 |
| 15 | 1737890081351424000 |
| 16 | 79498734605402112000 |
| 17 | 3871319396080840704000 |
| 18 | 200017645344178421760000 |
| 19 | 10925549584125028909056000 |