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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 3 |
| 3 | 6 |
| 4 | 9 |
| 5 | 18 |
| 6 | 45 |
| 7 | 118 |
| 8 | 336 |
| 9 | 954 |
| 10 | 2695 |
| 11 | 7590 |
| 12 | 21321 |
| 13 | 59890 |
| 14 | 168273 |
| 15 | 473966 |
| 16 | 1337476 |
| 17 | 3785154 |
| 18 | 10738373 |
| 19 | 30546502 |
| 20 | 87099571 |
| 21 | 248937978 |
| 22 | 712995733 |
| 23 | 2046236598 |
| 24 | 5883318437 |
| 25 | 16944709370 |
| 26 | 48880145967 |
| 27 | 141211579446 |
[1,2,3,6,9,18,45,118,336,954,2695,7590,21321, 59890,168273,473966,1337476,3785154,10738373, 30546502,87099571,248937978,712995733,2046236598, 5883318437,16944709370,48880145967,141211579446] |