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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 23 |
| 4 | 158 |
| 5 | 1212 |
| 6 | 10058 |
| 7 | 88811 |
| 8 | 826982 |
| 9 | 8085950 |
| 10 | 82922624 |
| 11 | 893003234 |
| 12 | 10129641140 |
| 13 | 121552747370 |
| 14 | 1550460365622 |
| 15 | 21115793548491 |
| 16 | 308004022741254 |
| 17 | 4817224946243142 |
| 18 | 80703099826887368 |
| 19 | 1444218797390453282 |
| 20 | 27501426760092853796 |
| 21 | 554910390616969332656 |
[1,1,4,23,158,1212,10058,88811,826982,8085950, 82922624,893003234,10129641140,121552747370, 1550460365622,21115793548491,308004022741254, 4817224946243142,80703099826887368, 1444218797390453282,27501426760092853796, 554910390616969332656] |