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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 21 |
| 3 | 102 |
| 4 | 476 |
| 5 | 2200 |
| 6 | 10123 |
| 7 | 46471 |
| 8 | 213000 |
| 9 | 975380 |
| 10 | 4464474 |
| 11 | 20429739 |
| 12 | 93474260 |
| 13 | 427645941 |
| 14 | 1956395954 |
| 15 | 8949898045 |
| 16 | 40942368765 |
| 17 | 187294120155 |
| 18 | 856787747966 |
| 19 | 3919414321141 |
| 20 | 17929510264717 |
| 21 | 82019155503670 |
| 22 | 375199231601451 |
[4,21,102,476,2200,10123,46471,213000,975380, 4464474,20429739,93474260,427645941,1956395954, 8949898045,40942368765,187294120155,856787747966, 3919414321141,17929510264717,82019155503670, 375199231601451] |