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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 52 |
| 4 | 175 |
| 5 | 582 |
| 6 | 1927 |
| 7 | 6370 |
| 8 | 21045 |
| 9 | 69514 |
| 10 | 229597 |
| 11 | 758316 |
| 12 | 2504557 |
| 13 | 8272000 |
| 14 | 27320571 |
| 15 | 90233728 |
| 16 | 298021771 |
| 17 | 984299058 |
| 18 | 3250918963 |
| 19 | 10737055966 |
| 20 | 35462086881 |
| 21 | 117123316630 |
| 22 | 386832036793 |
| 23 | 1277619427032 |
| 24 | 4219690317913 |
[1,4,15,52,175,582,1927,6370,21045,69514,229597, 758316,2504557,8272000,27320571,90233728, 298021771,984299058,3250918963,10737055966, 35462086881,117123316630,386832036793, 1277619427032,4219690317913] |