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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 21 |
| 5 | 90 |
| 6 | 450 |
| 7 | 2619 |
| 8 | 17334 |
| 9 | 129114 |
| 10 | 1067661 |
| 11 | 9713682 |
| 12 | 96393726 |
| 13 | 1036348587 |
| 14 | 11998603710 |
| 15 | 148842430470 |
| 16 | 1969461102357 |
| 17 | 27688474234602 |
| 18 | 412166988789642 |
| 19 | 6476330295597051 |
| 20 | 107117619952992966 |
| 21 | 1860296912926495938 |
| 22 | 33845967939906741213 |
| 23 | 643778989807702357314 |
[1,1,2,6,21,90,450,2619,17334,129114,1067661, 9713682,96393726,1036348587,11998603710, 148842430470,1969461102357,27688474234602, 412166988789642,6476330295597051, 107117619952992966,1860296912926495938, 33845967939906741213,643778989807702357314] |