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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 5 |
| 4 | 20 |
| 5 | 99 |
| 6 | 584 |
| 7 | 4038 |
| 8 | 31970 |
| 9 | 285070 |
| 10 | 2826941 |
| 11 | 30860774 |
| 12 | 367757553 |
| 13 | 4750201727 |
| 14 | 66106974037 |
| 15 | 986095696055 |
| 16 | 15695356495548 |
| 17 | 265513114049684 |
| 18 | 4757109960056837 |
| 19 | 89988663411075165 |
| 20 | 1792274212937247027 |
| 21 | 37488402287270750315 |
| 22 | 821620816796017277740 |
[1,1,2,5,20,99,584,4038,31970,285070,2826941, 30860774,367757553,4750201727,66106974037, 986095696055,15695356495548,265513114049684, 4757109960056837,89988663411075165, 1792274212937247027,37488402287270750315, 821620816796017277740] |