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 | 0 |
| 2 | 2 |
| 3 | 12 |
| 4 | 36 |
| 5 | 240 |
| 6 | 2280 |
| 7 | 15120 |
| 8 | 122640 |
| 9 | 1330560 |
| 10 | 13335840 |
| 11 | 136382400 |
| 12 | 1657212480 |
| 13 | 20860519680 |
| 14 | 262278656640 |
| 15 | 3585207225600 |
| 16 | 52249374777600 |
| 17 | 772773281280000 |
| 18 | 11907924610982400 |
| 19 | 193962388523904000 |
| 20 | 3253343368231756800 |
| 21 | 56051640629816832000 |