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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 3 |
| 5 | 6 |
| 6 | 16 |
| 7 | 44 |
| 8 | 136 |
| 9 | 457 |
| 10 | 1669 |
| 11 | 6547 |
| 12 | 27334 |
| 13 | 120465 |
| 14 | 557094 |
| 15 | 2692528 |
| 16 | 13564940 |
| 17 | 71102869 |
| 18 | 387132791 |
| 19 | 2185813423 |
| 20 | 12775466408 |
| 21 | 77154694819 |
| 22 | 480630407368 |
| 23 | 3083443893896 |
| 24 | 20344187534051 |
| 25 | 137884769704754 |
[1,0,1,1,3,6,16,44,136,457,1669,6547,27334,120465, 557094,2692528,13564940,71102869,387132791, 2185813423,12775466408,77154694819,480630407368, 3083443893896,20344187534051,137884769704754] |