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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 6 |
| 4 | 27 |
| 5 | 104 |
| 6 | 369 |
| 7 | 1242 |
| 8 | 4039 |
| 9 | 12828 |
| 10 | 40077 |
| 11 | 123758 |
| 12 | 379011 |
| 13 | 1153872 |
| 14 | 3498025 |
| 15 | 10572354 |
| 16 | 31884543 |
| 17 | 96010436 |
| 18 | 288788613 |
| 19 | 867967830 |
| 20 | 2607282235 |
| 21 | 7828953720 |
| 22 | 23501774241 |
| 23 | 70536546986 |
| 24 | 211674885687 |
| 25 | 635160738924 |
| 26 | 1905765565309 |
[0,0,1,6,27,104,369,1242,4039,12828,40077,123758, 379011,1153872,3498025,10572354,31884543,96010436, 288788613,867967830,2607282235,7828953720, 23501774241,70536546986,211674885687,635160738924, 1905765565309] |