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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 110 |
| 6 | 550 |
| 7 | 2922 |
| 8 | 16242 |
| 9 | 93520 |
| 10 | 553980 |
| 11 | 3359384 |
| 12 | 20777588 |
| 13 | 130696662 |
| 14 | 834244830 |
| 15 | 5393850898 |
| 16 | 35272830054 |
| 17 | 233016356788 |
| 18 | 1553427829684 |
| 19 | 10441803227652 |
| 20 | 70715551631992 |
| 21 | 482201548554776 |
| 22 | 3308810614160224 |
| 23 | 22836540660981088 |
| 24 | 158458108961055864 |
| 25 | 1104984826809182592 |
[0,2,2,6,24,110,550,2922,16242,93520,553980, 3359384,20777588,130696662,834244830,5393850898, 35272830054,233016356788,1553427829684, 10441803227652,70715551631992,482201548554776, 3308810614160224,22836540660981088, 158458108961055864,1104984826809182592] |