题目：

题解：

func countArrangement(n int) int {
    f := make([]int, 1<<n)
    f[0] = 1
    for mask := 1; mask < 1<<n; mask++ {
        num := bits.OnesCount(uint(mask))
        for i := 0; i < n; i++ {
            if mask>>i&1 > 0 && (num%(i+1) == 0 || (i+1)%num == 0) {
                f[mask] += f[mask^1<<i]
            }
        }
    }
    return f[1<<n-1]
}