// #pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
// #include <x86intrin.h>
using namespace std;
#if __cplusplus >= 202002L
using namespace numbers;
#endif



int main(){
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(ios::badbit | ios::failbit);
	cout << fixed << setprecision(15);
	int n;
	cin >> n;
	vector<vector<int>> div(n + 1);
	for(auto x = 1; x <= n; ++ x){
		for(auto y = x; y <= n; y += x){
			div[y].push_back(x);
		}
	}
	vector<vector<array<int, 2>>> update(n + 1);
	for(auto x = 1; x <= n; ++ x){
		for(auto d: div[x]){
			for(auto e: div[x]){
				if(x / d == e / gcd(d, e)){
					update[d].push_back({e, x});
				}
			}
		}
	}
	vector<double> p(n + 1);
	{
		vector<int> a(n + 1);
		copy_n(istream_iterator<int>(cin), n, a.begin() + 1);
		int sum = accumulate(a.begin(), a.end(), 0);
		for(auto i = 1; i <= n; ++ i){
			p[i] = 1.0 * a[i] / sum;
		}
	}
	vector<double> dp(n + 1);
	for(auto x = n; x >= 1; -- x){
		double self = 0;
		for(auto [y, obj]: update[x]){
			dp[x] += p[y];
			if(obj == x){
				self += p[y];
			}
			else{
				dp[x] += p[y] * dp[obj];
			}
		}
		dp[x] /= 1 - self;
	}
	cout << dp[1] << "\n";
	return 0;
}

/*

*/