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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 42 |
| 5 | 149 |
| 6 | 563 |
| 7 | 2167 |
| 8 | 8521 |
| 9 | 34010 |
| 10 | 137899 |
| 11 | 566278 |
| 12 | 2347387 |
| 13 | 9815176 |
| 14 | 41356830 |
| 15 | 175507147 |
| 16 | 749312195 |
| 17 | 3216195084 |
| 18 | 13872335903 |
| 19 | 60105398885 |
| 20 | 261496852724 |
| 21 | 1141895019478 |
| 22 | 5003444985964 |
| 23 | 21993343270089 |
| 24 | 96961107283936 |
| 25 | 428639320358383 |
| 26 | 1899717847605466 |
| 27 | 8439559063692215 |
[1,1,4,12,42,149,563,2167,8521,34010,137899, 566278,2347387,9815176,41356830,175507147, 749312195,3216195084,13872335903,60105398885, 261496852724,1141895019478,5003444985964, 21993343270089,96961107283936,428639320358383, 1899717847605466,8439559063692215] |