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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 9 |
| 4 | 44 |
| 5 | 250 |
| 6 | 1644 |
| 7 | 12348 |
| 8 | 104544 |
| 9 | 986256 |
| 10 | 10265760 |
| 11 | 116915040 |
| 12 | 1446526080 |
| 13 | 19323757440 |
| 14 | 277238626560 |
| 15 | 4251984710400 |
| 16 | 69426608025600 |
| 17 | 1202482800691200 |
| 18 | 22021300630425600 |
| 19 | 425162773111910400 |
[0,0,2,9,44,250,1644,12348,104544,986256,10265760, 116915040,1446526080,19323757440,277238626560, 4251984710400,69426608025600,1202482800691200, 22021300630425600,425162773111910400] |