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 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 54 |
| 6 | 486 |
| 7 | 9720 |
| 8 | 204120 |
| 9 | 6531840 |
| 10 | 241678080 |
| 11 | 13050616320 |
| 12 | 652530816000 |
| 13 | 50244872832000 |
| 14 | 4069834699392000 |
| 15 | 390704131141632000 |
| 16 | 41023933769871360000 |
| 17 | 5538231058932633600000 |
| 18 | 731046499779107635200000 |
| 19 | 124277904962448297984000000 |