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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 19 |
| 3 | 186 |
| 4 | 1365 |
| 5 | 8540 |
| 6 | 48348 |
| 7 | 255816 |
| 8 | 1289739 |
| 9 | 6273135 |
| 10 | 29683225 |
| 11 | 137447310 |
| 12 | 625482585 |
| 13 | 2806282440 |
| 14 | 12443418600 |
| 15 | 54633668400 |
| 16 | 237871030860 |
| 17 | 1028260382994 |
| 18 | 4417404967206 |
| 19 | 18874729444340 |
| 20 | 80265980340370 |
| 21 | 339907420551336 |
| 22 | 1434074601137640 |
[0,1,19,186,1365,8540,48348,255816,1289739, 6273135,29683225,137447310,625482585,2806282440, 12443418600,54633668400,237871030860, 1028260382994,4417404967206,18874729444340, 80265980340370,339907420551336,1434074601137640] |