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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 88 |
| 5 | 594 |
| 6 | 4404 |
| 7 | 35260 |
| 8 | 300918 |
| 9 | 2714187 |
| 10 | 25715364 |
| 11 | 254752536 |
| 12 | 2629587927 |
| 13 | 28202629918 |
| 14 | 313575278100 |
| 15 | 3607684547463 |
| 16 | 42880301468830 |
| 17 | 525812475574788 |
| 18 | 6643855672178904 |
| 19 | 86407881067891029 |
| 20 | 1155583581407910414 |
[1,1,3,15,88,594,4404,35260,300918,2714187, 25715364,254752536,2629587927,28202629918, 313575278100,3607684547463,42880301468830, 525812475574788,6643855672178904, 86407881067891029,1155583581407910414] |