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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 13 |
| 6 | 37 |
| 7 | 106 |
| 8 | 409 |
| 9 | 1896 |
| 10 | 12171 |
| 11 | 105070 |
| 12 | 1262179 |
| 13 | 20797001 |
| 14 | 467871368 |
| 15 | 14232552451 |
| 16 | 581460254000 |
| 17 | 31720840164949 |
[0,1,2,6,13,37,106,409,1896,12171,105070,1262179, 20797001,467871368,14232552451,581460254000, 31720840164949] |