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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 7 |
| 5 | 33 |
| 6 | 201 |
| 7 | 1479 |
| 8 | 12842 |
| 9 | 127952 |
| 10 | 1440989 |
| 11 | 18070767 |
| 12 | 249766088 |
| 13 | 3769280801 |
| 14 | 61654447712 |
| 15 | 1085974748430 |
| 16 | 20485430748783 |
| 17 | 411839042136379 |
| 18 | 8786499316562396 |
| 19 | 198174104269740313 |
| 20 | 4708919322491690592 |
[1,1,1,2,7,33,201,1479,12842,127952,1440989, 18070767,249766088,3769280801,61654447712, 1085974748430,20485430748783,411839042136379, 8786499316562396,198174104269740313, 4708919322491690592] |