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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 9 |
| 5 | 44 |
| 6 | 265 |
| 7 | 1854 |
| 8 | 14833 |
| 9 | 133496 |
| 10 | 1334961 |
| 11 | 14684570 |
| 12 | 176214841 |
| 13 | 2290792932 |
| 14 | 10930514688 |
| 15 | 52034548064 |
| 16 | 247272708868 |
| 17 | 1173385630596 |
| 18 | 5560837425792 |
| 19 | 26322368822528 |
| 20 | 124470922522980 |
| 21 | 589274182149120 |
| 22 | 2793967092494408 |
| 23 | 13269446868206480 |
| 24 | 63125696320334912 |
[1,0,1,2,9,44,265,1854,14833,133496,1334961, 14684570,176214841,2290792932,10930514688, 52034548064,247272708868,1173385630596, 5560837425792,26322368822528,124470922522980, 589274182149120,2793967092494408, 13269446868206480,63125696320334912] |