Submission #1584865

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Source Code Expand

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;

#define each(i,a) for (auto&& i : a)
#define FOR(i,a,b) for (ll i=(a),__last_##i=(b);i<__last_##i;i++)
#define RFOR(i,a,b) for (ll i=(b)-1,__last_##i=(a);i>=__last_##i;i--)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) RFOR(i,0,n)
#define __GET_MACRO3(_1, _2, _3, NAME, ...) NAME
#define rep(...) __GET_MACRO3(__VA_ARGS__, FOR, REP)(__VA_ARGS__)
#define rrep(...) __GET_MACRO3(__VA_ARGS__, RFOR, RREP)(__VA_ARGS__)
#define pb push_back
#define all(a) (a).begin(),(a).end()
#define chmin(x,v) x = min(x, v)
#define chmax(x,v) x = max(x, v)

const ll linf = 1e18;
const int inf = 1e9;
const double eps = 1e-12;
const double pi = acos(-1);

template<typename T>
istream& operator>>(istream& is, vector<T>& vec) {
    each(x,vec) is >> x;
    return is;
}
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& vec) {
    rep(i,vec.size()) {
        if (i) os << " ";
        os << vec[i];
    }
    return os;
}
template<typename T>
ostream& operator<<(ostream& os, const vector< vector<T> >& vec) {
    rep(i,vec.size()) {
        if (i) os << endl;
        os << vec[i];
    }
    return os;
}
double fact(ll n) {
    double res = 1;
    rep(i, n) res *= i + 1;
    return res;
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll n; cin >> n;
    vector<ll> c(n); cin >> c;
    double ans = 0;
    rep(i, n) {
        ll cnt = 0;
        rep(j, n) {
            if (i == j) continue;
            if (c[i] % c[j] == 0) ++cnt;
        }
        rep(i, cnt+1) {
            if (i % 2 == 1) continue;
            ans += 1 / double(cnt+1);
        }
    }
    cout << fixed << setprecision(10) << ans << endl;
}

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