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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 19 |
| 5 | 71 |
| 6 | 300 |
| 7 | 1370 |
| 8 | 6563 |
| 9 | 32272 |
| 10 | 161700 |
| 11 | 820166 |
| 12 | 4198764 |
| 13 | 21647353 |
| 14 | 112262033 |
| 15 | 585049063 |
| 16 | 3061951973 |
| 17 | 16084816384 |
| 18 | 84773694223 |
[1,1,2,6,19,71,300,1370,6563,32272,161700,820166, 4198764,21647353,112262033,585049063,3061951973, 16084816384,84773694223] |