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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 6 |
| 3 | 33 |
| 4 | 174 |
| 5 | 915 |
| 6 | 4854 |
| 7 | 25962 |
| 8 | 139836 |
| 9 | 757545 |
| 10 | 4123236 |
| 11 | 22527393 |
| 12 | 123451554 |
| 13 | 678148620 |
| 14 | 3732306474 |
| 15 | 20572095777 |
| 16 | 113524359906 |
| 17 | 627044542215 |
| 18 | 3465927182766 |
| 19 | 19168307134278 |
| 20 | 106056611012784 |
| 21 | 587001832650825 |
[0,6,33,174,915,4854,25962,139836,757545,4123236, 22527393,123451554,678148620,3732306474, 20572095777,113524359906,627044542215, 3465927182766,19168307134278,106056611012784, 587001832650825] |