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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 10 |
| 6 | 24 |
| 7 | 66 |
| 8 | 176 |
| 9 | 498 |
| 10 | 1416 |
| 11 | 4122 |
| 12 | 12068 |
| 13 | 35930 |
| 14 | 107632 |
| 15 | 325346 |
| 16 | 989600 |
| 17 | 3029914 |
| 18 | 9323248 |
| 19 | 28831066 |
| 20 | 89525028 |
| 21 | 279074634 |
| 22 | 872958488 |
| 23 | 2739387258 |
| 24 | 8621086800 |
| 25 | 27203628682 |
| 26 | 86050008056 |
| 27 | 272807862746 |
| 28 | 866704248868 |
| 29 | 2758862542482 |
| 30 | 8797833793728 |
[0,2,1,2,4,10,24,66,176,498,1416,4122,12068,35930, 107632,325346,989600,3029914,9323248,28831066, 89525028,279074634,872958488,2739387258, 8621086800,27203628682,86050008056,272807862746, 866704248868,2758862542482,8797833793728] |