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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 8 |
| 3 | 40 |
| 4 | 222 |
| 5 | 1296 |
| 6 | 7770 |
| 7 | 47324 |
| 8 | 291260 |
| 9 | 1806220 |
| 10 | 11266718 |
| 11 | 70609316 |
| 12 | 444231564 |
| 13 | 2803975860 |
| 14 | 17748069294 |
| 15 | 112609964308 |
| 16 | 716010467122 |
| 17 | 4561107325336 |
| 18 | 29103104031990 |
| 19 | 185973253609716 |
| 20 | 1189979068401564 |
| 21 | 7623432519587692 |
| 22 | 48891854980251090 |
| 23 | 313874287333373820 |
[1,2,8,40,222,1296,7770,47324,291260,1806220, 11266718,70609316,444231564,2803975860, 17748069294,112609964308,716010467122, 4561107325336,29103104031990,185973253609716, 1189979068401564,7623432519587692, 48891854980251090,313874287333373820] |