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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 5 |
| 4 | 18 |
| 5 | 164 |
| 6 | 1538 |
| 7 | 20018 |
| 8 | 408404 |
| 9 | 7759748 |
| 10 | 148728578 |
| 11 | 6976017044 |
| 12 | 7317446132 |
[1,2,5,18,164,1538,20018,408404,7759748,148728578, 6976017044,7317446132] |