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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 7 |
| 5 | 30 |
| 6 | 107 |
| 7 | 450 |
| 8 | 1935 |
| 9 | 8666 |
| 10 | 38990 |
| 11 | 177500 |
| 12 | 813490 |
| 13 | 3756250 |
| 14 | 17439507 |
| 15 | 81385410 |
| 16 | 381473625 |
| 17 | 1795156250 |
| 18 | 8477078967 |
| 19 | 40154687500 |
| 20 | 190734746125 |
| 21 | 908261160564 |
| 22 | 4334882723750 |
| 23 | 20732050781250 |
| 24 | 99341076252470 |
| 25 | 476837167968750 |
| 26 | 2292486345026923 |
[0,0,2,7,30,107,450,1935,8666,38990,177500,813490, 3756250,17439507,81385410,381473625,1795156250, 8477078967,40154687500,190734746125,908261160564, 4334882723750,20732050781250,99341076252470, 476837167968750,2292486345026923] |