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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 2 |
| 4 | 12 |
| 5 | 30 |
| 6 | 110 |
| 7 | 336 |
| 8 | 1118 |
| 9 | 3570 |
| 10 | 11628 |
| 11 | 37510 |
| 12 | 121574 |
| 13 | 393120 |
| 14 | 1272646 |
| 15 | 4117594 |
| 16 | 13326060 |
| 17 | 43122030 |
| 18 | 139549054 |
| 19 | 451585008 |
| 20 | 1461368206 |
| 21 | 4729073250 |
| 22 | 15303624492 |
| 23 | 49523533622 |
| 24 | 160261578742 |
| 25 | 518617270080 |
| 26 | 1678280890550 |
[1,0,2,2,12,30,110,336,1118,3570,11628,37510, 121574,393120,1272646,4117594,13326060,43122030, 139549054,451585008,1461368206,4729073250, 15303624492,49523533622,160261578742,518617270080, 1678280890550] |