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 | 5 |
| 3 | 20 |
| 4 | 150 |
| 5 | 624 |
| 6 | 9600 |
| 7 | 36000 |
| 8 | 811440 |
| 9 | 6572160 |
| 10 | 105235200 |
| 11 | 442713600 |
| 12 | 39437798400 |
| 13 | 81430272000 |
| 14 | 4956708556800 |
| 15 | 137741700096000 |
| 16 | 3014189418240000 |
| 17 | 6067609067520000 |
| 18 | 1977977787641856000 |
| 19 | 2317659281473536000 |
| 20 | 1297953221362237440000 |