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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 21 |
| 4 | 79 |
| 5 | 307 |
| 6 | 1251 |
| 7 | 5157 |
| 8 | 21770 |
| 9 | 93084 |
| 10 | 402471 |
| 11 | 1757704 |
| 12 | 7735990 |
| 13 | 34272982 |
| 14 | 152769404 |
| 15 | 684287508 |
| 16 | 3078918306 |
| 17 | 13908382920 |
| 18 | 63045086927 |
| 19 | 286686826482 |
| 20 | 1307343149661 |
| 21 | 5976997737308 |
| 22 | 27390316189542 |
| 23 | 125786903175386 |
| 24 | 578797240061250 |
| 25 | 2668110621923576 |
| 26 | 12319849450174142 |
| 27 | 56974513972803076 |
[1,2,6,21,79,307,1251,5157,21770,93084,402471, 1757704,7735990,34272982,152769404,684287508, 3078918306,13908382920,63045086927,286686826482, 1307343149661,5976997737308,27390316189542, 125786903175386,578797240061250,2668110621923576, 12319849450174142,56974513972803076] |