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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 30 |
| 5 | 144 |
| 6 | 758 |
| 7 | 4080 |
| 8 | 22702 |
| 9 | 128832 |
| 10 | 744300 |
| 11 | 4359972 |
| 12 | 25842414 |
| 13 | 154689912 |
| 14 | 933828324 |
| 15 | 5678696556 |
| 16 | 34754244174 |
| 17 | 213901762464 |
| 18 | 1323104558204 |
| 19 | 8220846355956 |
| 20 | 51284447272084 |
| 21 | 321095305733280 |
| 22 | 2017050339848388 |
| 23 | 12708912192988128 |
| 24 | 80296949632284814 |
| 25 | 508618518515268720 |
[1,0,2,6,30,144,758,4080,22702,128832,744300, 4359972,25842414,154689912,933828324,5678696556, 34754244174,213901762464,1323104558204, 8220846355956,51284447272084,321095305733280, 2017050339848388,12708912192988128, 80296949632284814,508618518515268720] |