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 | 6 |
| 3 | 90 |
| 4 | 2520 |
| 5 | 113400 |
| 6 | 7484400 |
| 7 | 681080400 |
| 8 | 81729648000 |
| 9 | 7580424852000 |
| 10 | 569159625434400 |
| 11 | 36636506215016400 |
| 12 | 2141931687266957040 |