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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 17 |
| 6 | 51 |
| 7 | 156 |
| 8 | 488 |
| 9 | 1552 |
| 10 | 5006 |
| 11 | 16337 |
| 12 | 53849 |
| 13 | 179015 |
| 14 | 599535 |
| 15 | 2020924 |
| 16 | 6851150 |
| 17 | 23344138 |
| 18 | 79902364 |
| 19 | 274606264 |
| 20 | 947240592 |
| 21 | 3278404274 |
| 22 | 11381240074 |
| 23 | 39621423949 |
| 24 | 138288477617 |
| 25 | 483805404673 |
| 26 | 1696318159457 |
| 27 | 5959737806635 |
[1,0,1,2,6,17,51,156,488,1552,5006,16337,53849, 179015,599535,2020924,6851150,23344138,79902364, 274606264,947240592,3278404274,11381240074, 39621423949,138288477617,483805404673, 1696318159457,5959737806635] |