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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 6 |
| 4 | 25 |
| 5 | 126 |
| 6 | 733 |
| 7 | 5086 |
| 8 | 40423 |
| 9 | 363262 |
| 10 | 3629743 |
| 11 | 39920638 |
| 12 | 479011993 |
| 13 | 6227066878 |
| 14 | 87178426333 |
| 15 | 1307675013118 |
| 16 | 20922791915023 |
| 17 | 355687438417918 |
| 18 | 6402373740187423 |
| 19 | 121645100594626558 |
| 20 | 2432902008831369073 |
[0,0,1,6,25,126,733,5086,40423,363262,3629743, 39920638,479011993,6227066878,87178426333, 1307675013118,20922791915023,355687438417918, 6402373740187423,121645100594626558, 2432902008831369073] |