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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 85 |
| 5 | 413 |
| 6 | 2044 |
| 7 | 10248 |
| 8 | 51876 |
| 9 | 264550 |
| 10 | 1357070 |
| 11 | 6994780 |
| 12 | 36196706 |
| 13 | 187938842 |
| 14 | 978599560 |
| 15 | 5108177816 |
| 16 | 26721644973 |
| 17 | 140050505085 |
| 18 | 735254208670 |
| 19 | 3865837887450 |
| 20 | 20353393741065 |
| 21 | 107290306033845 |
| 22 | 566194674179160 |
| 23 | 2990958274811520 |
| 24 | 15814562990604300 |
| 25 | 83690040760923168 |
[1,1,4,18,85,413,2044,10248,51876,264550,1357070, 6994780,36196706,187938842,978599560,5108177816, 26721644973,140050505085,735254208670, 3865837887450,20353393741065,107290306033845, 566194674179160,2990958274811520, 15814562990604300,83690040760923168] |