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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 10 |
| 5 | 48 |
| 6 | 288 |
| 7 | 1984 |
| 8 | 15660 |
| 9 | 139312 |
| 10 | 1380484 |
| 11 | 15080152 |
| 12 | 180017780 |
| 13 | 2331038048 |
| 14 | 32537274756 |
| 15 | 486942025288 |
| 16 | 7777172706308 |
| 17 | 132025174277392 |
| 18 | 2373753512469972 |
| 19 | 45059504242538328 |
| 20 | 900498975768121972 |
| 21 | 18898334957168597184 |
| 22 | 415537355533831049572 |
| 23 | 9552918187197519923176 |
[1,0,1,2,10,48,288,1984,15660,139312,1380484, 15080152,180017780,2331038048,32537274756, 486942025288,7777172706308,132025174277392, 2373753512469972,45059504242538328, 900498975768121972,18898334957168597184, 415537355533831049572,9552918187197519923176] |