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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 60 |
| 4 | 422 |
| 5 | 1840 |
| 6 | 6456 |
| 7 | 20032 |
| 8 | 57440 |
| 9 | 155904 |
| 10 | 406400 |
| 11 | 1027072 |
| 12 | 2532864 |
| 13 | 6123520 |
| 14 | 14563328 |
| 15 | 34160640 |
| 16 | 79192064 |
| 17 | 181731328 |
| 18 | 413368320 |
| 19 | 932970496 |
| 20 | 2091253760 |
| 21 | 4658823168 |
| 22 | 10321657856 |
| 23 | 22754099200 |
| 24 | 49935286272 |
| 25 | 109135790080 |
[0,3,60,422,1840,6456,20032,57440,155904,406400, 1027072,2532864,6123520,14563328,34160640, 79192064,181731328,413368320,932970496,2091253760, 4658823168,10321657856,22754099200,49935286272, 109135790080] |