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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 52 |
| 5 | 190 |
| 6 | 850 |
| 7 | 3433 |
| 8 | 15725 |
| 9 | 67088 |
| 10 | 312593 |
| 11 | 1379704 |
| 12 | 6507124 |
| 13 | 29391737 |
| 14 | 139840831 |
| 15 | 642273010 |
| 16 | 3075896765 |
| 17 | 14305813433 |
| 18 | 68859801542 |
| 19 | 323395442425 |
| 20 | 1562939548509 |
| 21 | 7397157690171 |
| 22 | 35867819722084 |
| 23 | 170821813960206 |
| 24 | 830563578845814 |
| 25 | 3976006093325299 |
| 26 | 19376694311869116 |
| 27 | 93158191980353477 |
[1,1,4,12,52,190,850,3433,15725,67088,312593, 1379704,6507124,29391737,139840831,642273010, 3075896765,14305813433,68859801542,323395442425, 1562939548509,7397157690171,35867819722084, 170821813960206,830563578845814,3976006093325299, 19376694311869116,93158191980353477] |