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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 25 |
| 5 | 189 |
| 6 | 1156 |
| 7 | 6996 |
| 8 | 43681 |
| 9 | 268632 |
| 10 | 1664100 |
| 11 | 10278914 |
| 12 | 63568729 |
| 13 | 392903168 |
| 14 | 2429109796 |
[0,1,4,25,189,1156,6996,43681,268632,1664100, 10278914,63568729,392903168,2429109796] |