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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 7 |
| 3 | 30 |
| 4 | 144 |
| 5 | 742 |
| 6 | 4012 |
| 7 | 22458 |
| 8 | 129035 |
| 9 | 756602 |
| 10 | 4509141 |
| 11 | 27233726 |
| 12 | 166320987 |
| 13 | 1025356360 |
| 14 | 6372494608 |
| 15 | 39882831334 |
| 16 | 251146002084 |
| 17 | 1590079213920 |
| 18 | 10115878798130 |
| 19 | 64634124182670 |
| 20 | 414578955678690 |
| 21 | 2668578654593970 |
| 22 | 17232252926468640 |
| 23 | 111602332042716450 |
[1,2,7,30,144,742,4012,22458,129035,756602, 4509141,27233726,166320987,1025356360,6372494608, 39882831334,251146002084,1590079213920, 10115878798130,64634124182670,414578955678690, 2668578654593970,17232252926468640, 111602332042716450] |