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 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 12 |
| 4 | 96 |
| 5 | 1000 |
| 6 | 12960 |
| 7 | 201684 |
| 8 | 3670016 |
| 9 | 76527504 |
| 10 | 1800000000 |
| 11 | 47158953820 |
| 12 | 1362182012928 |
| 13 | 43011849456888 |
| 14 | 1474041721757696 |
| 15 | 54493461914062500 |
| 16 | 2161727821137838080 |
| 17 | 91597537648314105376 |
| 18 | 4128944057284204560384 |
| 19 | 197293926880252878693804 |
| 20 | 9961472000000000000000000 |