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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 80 |
| 5 | 294 |
| 6 | 1168 |
| 7 | 4700 |
| 8 | 19616 |
| 9 | 80936 |
| 10 | 341652 |
| 11 | 1451138 |
| 12 | 6240682 |
| 13 | 26900956 |
| 14 | 116808978 |
| 15 | 509503870 |
| 16 | 2235781132 |
| 17 | 9846065742 |
| 18 | 43506965704 |
| 19 | 192855619628 |
| 20 | 857932000186 |
| 21 | 3827546695256 |
| 22 | 17114951919858 |
| 23 | 76699514623644 |
| 24 | 344535118116958 |
| 25 | 1551000876073158 |
| 26 | 6994631039368602 |
| 27 | 31595691327084332 |
[1,2,6,20,80,294,1168,4700,19616,80936,341652, 1451138,6240682,26900956,116808978,509503870, 2235781132,9846065742,43506965704,192855619628, 857932000186,3827546695256,17114951919858, 76699514623644,344535118116958,1551000876073158, 6994631039368602,31595691327084332] |