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 | 2 |
| 2 | 10 |
| 3 | 60 |
| 4 | 408 |
| 5 | 3120 |
| 6 | 26640 |
| 7 | 252000 |
| 8 | 2620800 |
| 9 | 29756160 |
| 10 | 366508800 |
| 11 | 4869849600 |
| 12 | 69455232000 |
| 13 | 1058593536000 |
| 14 | 17174123366400 |
| 15 | 295534407168000 |
| 16 | 5377157001216000 |
| 17 | 103149354147840000 |
| 18 | 2080771454361600000 |