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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 91 |
| 5 | 603 |
| 6 | 4213 |
| 7 | 30537 |
| 8 | 227475 |
| 9 | 1730787 |
| 10 | 13393689 |
| 11 | 105089229 |
| 12 | 834086421 |
| 13 | 6684761125 |
| 14 | 54022715451 |
| 15 | 439742222071 |
| 16 | 3602118427251 |
| 17 | 29671013856627 |
| 18 | 245613376802185 |
| 19 | 2042162142208813 |
| 20 | 17047255430494497 |
| 21 | 142816973618414817 |
[1,1,3,15,91,603,4213,30537,227475,1730787, 13393689,105089229,834086421,6684761125, 54022715451,439742222071,3602118427251, 29671013856627,245613376802185,2042162142208813, 17047255430494497,142816973618414817] |