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| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 12 |
| 3 | 56 |
| 4 | 254 |
| 5 | 1620 |
| 6 | 10804 |
| 7 | 77614 |
| 8 | 582800 |
| 9 | 4548410 |
| 10 | 36400976 |
| 11 | 298182320 |
| 12 | 2487444740 |
| 13 | 21066301710 |
[3,12,56,254,1620,10804,77614,582800,4548410, 36400976,298182320,2487444740,21066301710] |