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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 10 |
| 4 | 21 |
| 5 | 47 |
| 6 | 102 |
| 7 | 256 |
| 8 | 754 |
| 9 | 2169 |
| 10 | 5999 |
| 11 | 17237 |
| 12 | 49510 |
| 13 | 132956 |
| 14 | 339522 |
| 15 | 900236 |
| 16 | 2620855 |
| 17 | 8077245 |
| 18 | 24619352 |
| 19 | 71983144 |
| 20 | 205409149 |
| 21 | 584195761 |
| 22 | 1647027286 |
| 23 | 4572955010 |
| 24 | 12705583667 |
| 25 | 36182897964 |
| 26 | 106766407391 |
| 27 | 326242477740 |
[2,4,10,21,47,102,256,754,2169,5999,17237,49510, 132956,339522,900236,2620855,8077245,24619352, 71983144,205409149,584195761,1647027286, 4572955010,12705583667,36182897964,106766407391, 326242477740] |