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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 54 |
| 4 | 236 |
| 5 | 1288 |
| 6 | 7092 |
| 7 | 42614 |
| 8 | 269352 |
| 9 | 1743560 |
| 10 | 11922442 |
| 11 | 80209268 |
| 12 | 562280115 |
| 13 | 3772081046 |
[1,4,12,54,236,1288,7092,42614,269352,1743560, 11922442,80209268,562280115,3772081046] |