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 | 2 |
| 3 | 9 |
| 4 | 48 |
| 5 | 320 |
| 6 | 2580 |
| 7 | 24150 |
| 8 | 258720 |
| 9 | 3117744 |
| 10 | 41741280 |
| 11 | 614774160 |
| 12 | 9877412160 |
| 13 | 171923225760 |
| 14 | 3222634615200 |
| 15 | 64721762305200 |
| 16 | 1386495651340800 |
| 17 | 31558444491974400 |
| 18 | 760564843136017920 |
| 19 | 19348085890139086080 |
| 20 | 518103061345155686400 |
| 21 | 14567452481227893811200 |