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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 4 |
| 5 | 20 |
| 6 | 189 |
| 7 | 1642 |
| 8 | 26451 |
| 9 | 307874 |
| 10 | 7027942 |
| 11 | 98057806 |
| 12 | 2850280812 |
| 13 | 44974137856 |
[1,1,1,4,20,189,1642,26451,307874,7027942, 98057806,2850280812,44974137856] |