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) |
|---|---|
| 3 | 1 |
| 4 | 9 |
| 5 | 132 |
| 6 | 2700 |
| 7 | 70920 |
| 8 | 2275560 |
| 9 | 86264640 |
| 10 | 3772681920 |
| 11 | 186972105600 |
| 12 | 10355595465600 |
| 13 | 633892275878400 |
| 14 | 42495895579737600 |
| 15 | 3096545573029708800 |
| 16 | 243680880958010496000 |
| 17 | 20596410256606119936000 |
| 18 | 1860881636529774802944000 |
| 19 | 178975197401013144907776000 |
| 20 | 18256461815785805072068608000 |