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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 48 |
| 3 | 448 |
| 4 | 3840 |
| 5 | 31744 |
| 6 | 258048 |
| 7 | 2080768 |
| 8 | 16711680 |
| 9 | 133955584 |
| 10 | 1072693248 |
| 11 | 8585740288 |
| 12 | 68702699520 |
| 13 | 549688705024 |
| 14 | 4397778075648 |
| 15 | 35183298347008 |
| 16 | 281470681743360 |
| 17 | 2251782633816064 |
| 18 | 18014329790005248 |
| 19 | 144114913197948928 |
| 20 | 1152920405095219200 |
| 21 | 9223367638808264704 |
[0,4,48,448,3840,31744,258048,2080768,16711680, 133955584,1072693248,8585740288,68702699520, 549688705024,4397778075648,35183298347008, 281470681743360,2251782633816064, 18014329790005248,144114913197948928, 1152920405095219200,9223367638808264704] |