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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 13 |
| 3 | 149 |
| 4 | 1750 |
| 5 | 21894 |
| 6 | 295500 |
| 7 | 4320420 |
| 8 | 68487120 |
| 9 | 1176564240 |
| 10 | 21883528800 |
| 11 | 440117949600 |
| 12 | 9557404012800 |
| 13 | 223720054790400 |
| 14 | 5634130146624000 |
| 15 | 152315974848038400 |
| 16 | 4409413104676608000 |
| 17 | 136318041562123008000 |
| 18 | 4487618159996944896000 |
| 19 | 156852415886275726848000 |
| 20 | 5803748680475885432832000 |
[0,1,13,149,1750,21894,295500,4320420,68487120, 1176564240,21883528800,440117949600,9557404012800, 223720054790400,5634130146624000, 152315974848038400,4409413104676608000, 136318041562123008000,4487618159996944896000, 156852415886275726848000, 5803748680475885432832000] |