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 | 3 |
| 3 | 12 |
| 4 | 72 |
| 5 | 504 |
| 6 | 4536 |
| 7 | 45360 |
| 8 | 544320 |
| 9 | 7076160 |
| 10 | 106142400 |
| 11 | 1698278400 |
| 12 | 30569011200 |
| 13 | 580811212800 |
| 14 | 12197035468800 |
| 15 | 268334780313600 |
| 16 | 6440034727526400 |
| 17 | 161000868188160000 |
| 18 | 4347023441080320000 |
| 19 | 121716656350248960000 |
| 20 | 3651499690507468800000 |