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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 26 |
| 5 | 120 |
| 6 | 524 |
| 7 | 2174 |
| 8 | 8816 |
| 9 | 35036 |
| 10 | 137164 |
| 11 | 530660 |
| 12 | 2033212 |
| 13 | 7728080 |
| 14 | 29176258 |
| 15 | 109517952 |
| 16 | 409053414 |
| 17 | 1521210528 |
| 18 | 5635589250 |
| 19 | 20807397706 |
| 20 | 76591784712 |
| 21 | 281168155840 |
| 22 | 1029636092960 |
| 23 | 3762126788080 |
| 24 | 13718306165240 |
| 25 | 49929760704254 |
[0,0,6,26,120,524,2174,8816,35036,137164,530660, 2033212,7728080,29176258,109517952,409053414, 1521210528,5635589250,20807397706,76591784712, 281168155840,1029636092960,3762126788080, 13718306165240,49929760704254] |