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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 1 |
| 4 | 6 |
| 5 | 10 |
| 6 | 15 |
| 7 | 60 |
| 8 | 128 |
| 9 | 267 |
| 10 | 810 |
| 11 | 1878 |
| 12 | 4579 |
| 13 | 12408 |
| 14 | 30552 |
| 15 | 77105 |
| 16 | 200876 |
| 17 | 505862 |
| 18 | 1288511 |
| 19 | 3311514 |
| 20 | 8411436 |
| 21 | 21467751 |
| 22 | 54921524 |
| 23 | 139947224 |
| 24 | 357287611 |
| 25 | 912689144 |
| 26 | 2328342518 |
| 27 | 5944207749 |
| 28 | 15177139978 |
| 29 | 38734201690 |
| 30 | 98882999903 |
| 31 | 252436571832 |
[0,4,1,6,10,15,60,128,267,810,1878,4579,12408, 30552,77105,200876,505862,1288511,3311514,8411436, 21467751,54921524,139947224,357287611,912689144, 2328342518,5944207749,15177139978,38734201690, 98882999903,252436571832] |