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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 18 |
| 5 | 65 |
| 6 | 295 |
| 7 | 1652 |
| 8 | 11032 |
| 9 | 85353 |
| 10 | 749203 |
| 11 | 7347384 |
| 12 | 79564496 |
| 13 | 942541041 |
| 14 | 12121319327 |
| 15 | 168145213732 |
| 16 | 2502276609008 |
| 17 | 39761200642225 |
| 18 | 671855234838915 |
| 19 | 12028625060491336 |
| 20 | 227451564319791336 |
| 21 | 4529507975800063337 |
| 22 | 94751047516476943359 |
| 23 | 2077192015403191663844 |
[0,0,2,6,18,65,295,1652,11032,85353,749203, 7347384,79564496,942541041,12121319327, 168145213732,2502276609008,39761200642225, 671855234838915,12028625060491336, 227451564319791336,4529507975800063337, 94751047516476943359,2077192015403191663844] |