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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 54 |
| 4 | 220 |
| 5 | 1130 |
| 6 | 5568 |
| 7 | 26966 |
| 8 | 132037 |
| 9 | 589652 |
| 10 | 2601811 |
| 11 | 10147378 |
| 12 | 38356054 |
| 13 | 129698048 |
[1,4,12,54,220,1130,5568,26966,132037,589652, 2601811,10147378,38356054,129698048] |