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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 17 |
| 4 | 57 |
| 5 | 207 |
| 6 | 786 |
| 7 | 3057 |
| 8 | 12168 |
| 9 | 49161 |
| 10 | 200973 |
| 11 | 830381 |
| 12 | 3462433 |
| 13 | 14543365 |
| 14 | 61455313 |
| 15 | 261051074 |
| 16 | 1114132113 |
| 17 | 4775036853 |
| 18 | 20540793414 |
| 19 | 88645205402 |
| 20 | 383652117835 |
| 21 | 1664756627492 |
| 22 | 7241001588378 |
| 23 | 31563853315709 |
| 24 | 137860267982920 |
[2,4,17,57,207,786,3057,12168,49161,200973,830381, 3462433,14543365,61455313,261051074,1114132113, 4775036853,20540793414,88645205402,383652117835, 1664756627492,7241001588378,31563853315709, 137860267982920] |