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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 10 |
| 5 | 36 |
| 6 | 120 |
| 7 | 368 |
| 8 | 1089 |
| 9 | 3304 |
| 10 | 10168 |
| 11 | 31312 |
| 12 | 95880 |
| 13 | 293120 |
| 14 | 896824 |
| 15 | 2746569 |
| 16 | 8411818 |
| 17 | 25756220 |
| 18 | 78853410 |
| 19 | 241421436 |
| 20 | 739183568 |
| 21 | 2263249600 |
| 22 | 6929580817 |
| 23 | 21216729488 |
| 24 | 64960656448 |
| 25 | 198894856144 |
| 26 | 608971496032 |
| 27 | 1864533223584 |
| 28 | 5708777321872 |
[0,1,2,4,10,36,120,368,1089,3304,10168,31312, 95880,293120,896824,2746569,8411818,25756220, 78853410,241421436,739183568,2263249600, 6929580817,21216729488,64960656448,198894856144, 608971496032,1864533223584,5708777321872] |