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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 72 |
| 5 | 650 |
| 6 | 6480 |
| 7 | 80906 |
| 8 | 1121512 |
| 9 | 18069264 |
| 10 | 320204160 |
| 11 | 6348340152 |
| 12 | 136915211664 |
| 13 | 3230148306216 |
| 14 | 82078412377416 |
| 15 | 2248247450065080 |
| 16 | 65771634671679360 |
| 17 | 2052879248516927232 |
| 18 | 67955959831214467584 |
| 19 | 2381716543764159438336 |
[1,1,2,12,72,650,6480,80906,1121512,18069264, 320204160,6348340152,136915211664,3230148306216, 82078412377416,2248247450065080,65771634671679360, 2052879248516927232,67955959831214467584, 2381716543764159438336] |