#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout << fixed << setprecision(100);
    int test_cases;
    cin >> test_cases;
    auto solve_costs = [&](vector<ll>& a, vector<ld>& cost) -> ld {
        int n = (int) a.size();
        vector<ld> pre(n);
        for (int i = 0; i < n; i++) {
            if (i == 0) {
                pre[i] = cost[i];
            } else {
                pre[i] = pre[i - 1] + cost[i];
            }
        }
        auto sum = [&](int l, int r) -> ld {
            return pre[r] - (l == 0 ? 0 : pre[l - 1]);
        };
        vector<ld> mult(n);
        for (int i = 0; i < (n + 1) / 2; i++) {
            if (i == 0) {
                mult[i] = sum(0, n - 1);
            } else {
                mult[i] = mult[i - 1] + sum(i, n - 1 - i);
            }
        }
        for(int i = (n + 1) / 2; i < n; i++) {
            mult[i] = mult[n - 1 - i];
        }
        for (int i = 0; i < n; i++) {
            mult[i] -= cost[0];
        }
        ld ret = 0;
        for (int i = 0; i < n; i++) {
            ret += a[i] * mult[i];
        }
        return ret;
    };
    auto solve_case = [&](int tc) {
        int n;
        cin >> n;
        vector<ll> a(n);
        for (int i = 0; i < n; i++) {
            cin >> a[i];
        }
        vector<ll> pre(n);
        for (int i = 0; i < n; i++) {
            if (i == 0) {
                pre[i] = a[i];
            } else {
                pre[i] = pre[i - 1] + a[i];
            }
        }
        auto small_choose = [&](ll x, ll y) -> ld {
            if (y == 0) {
                return 1;
            } else if (y == 1) {
                return x;
            } else {
                return x * (x - 1) / 2;
            }
        };
        auto sum = [&](int l, int r) -> ll {
            return pre[r] - (l == 0 ? 0 : pre[l - 1]);
        };
        auto evaluate = [&](int l, int r) -> ld {
            int bad = (l != 0) + (r != n - 1);
            int good = r - l;
            return sum(l, r) / small_choose(bad + good, bad);
        };
        ld ans = 0;
        for (int r = 1; r < n; r++) {
            ans += evaluate(0, r);
        }
        for (int l = 1; l < n - 1; l++) {
            ans += evaluate(l, n - 1);
        }
        vector<ll> shrink(n - 2);
        vector<ld> cost1(n - 2);
        vector<ld> cost2(n - 2);
        for (int i = 1; i < n - 1; i++) {
            shrink[i - 1] = a[i];
        }
        for (int i = 1; i < n - 1; i++) {
            cost1[i - 1] = ((ld) 1) / i;
            cost2[i - 1] = ((ld) 1) / (i + 1);
        }
        ans += 2 * solve_costs(shrink, cost1);
        ans -= 2 * solve_costs(shrink, cost2);
        cout << ans << '\n';
    };
    for (int tc = 1; tc <= test_cases; tc++) {
        cout << "Case #" << tc << ": ";
        solve_case(tc);
    }
}