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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 18 |
| 4 | 174 |
| 5 | 1538 |
| 6 | 13722 |
| 7 | 123415 |
| 8 | 1108310 |
| 9 | 9952342 |
| 10 | 89374736 |
| 11 | 802604215 |
| 12 | 7207554901 |
| 13 | 64725391117 |
| 14 | 581247882251 |
| 15 | 5219730484108 |
| 16 | 46874298003145 |
| 17 | 420941238200854 |
| 18 | 3780142499106704 |
| 19 | 33946489479324642 |
| 20 | 304846748037181812 |
[0,2,18,174,1538,13722,123415,1108310,9952342, 89374736,802604215,7207554901,64725391117, 581247882251,5219730484108,46874298003145, 420941238200854,3780142499106704, 33946489479324642,304846748037181812] |