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| n | a(n) |
|---|---|
| 0 | 4 |
| 1 | 24 |
| 2 | 120 |
| 3 | 560 |
| 4 | 2520 |
| 5 | 11088 |
| 6 | 48048 |
| 7 | 205920 |
| 8 | 875160 |
| 9 | 3695120 |
| 10 | 15519504 |
| 11 | 64899744 |
| 12 | 270415600 |
| 13 | 1123264800 |
| 14 | 4653525600 |
| 15 | 19234572480 |
| 16 | 79342611480 |
| 17 | 326704870800 |
| 18 | 1343120024400 |
| 19 | 5513861152800 |
| 20 | 22606830726480 |
| 21 | 92580354403680 |
| 22 | 378737813469600 |
[4,24,120,560,2520,11088,48048,205920,875160, 3695120,15519504,64899744,270415600,1123264800, 4653525600,19234572480,79342611480,326704870800, 1343120024400,5513861152800,22606830726480, 92580354403680,378737813469600] |