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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 18 |
| 5 | 36 |
| 6 | 138 |
| 7 | 334 |
| 8 | 1066 |
| 9 | 3096 |
| 10 | 9490 |
| 11 | 26826 |
| 12 | 80468 |
| 13 | 235718 |
| 14 | 699056 |
| 15 | 2055466 |
| 16 | 6074498 |
| 17 | 17857906 |
| 18 | 52725190 |
| 19 | 155445504 |
| 20 | 458505084 |
| 21 | 1351257730 |
| 22 | 3984941402 |
| 23 | 11748306100 |
| 24 | 34643781158 |
| 25 | 102144907886 |
| 26 | 301179533022 |
| 27 | 887996181502 |
| 28 | 2618324249106 |
| 29 | 7720149428450 |
[1,0,2,4,18,36,138,334,1066,3096,9490,26826,80468, 235718,699056,2055466,6074498,17857906,52725190, 155445504,458505084,1351257730,3984941402, 11748306100,34643781158,102144907886,301179533022, 887996181502,2618324249106,7720149428450] |