#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef tuple<int, int, int> tii;

inline int rd() {
    int x = 0;
    bool f = 0;
    char c = getchar();
    for (; !isdigit(c); c = getchar()) f |= (c == '-');
    for (; isdigit(c); c = getchar()) x = x * 10 + (c ^ 48);
    return f ? -x : x;
}

#define eb emplace_back
#define all(s) (s).begin(), (s).end()
#define rep(i, a, b) for (int i = (a); i <= (b); ++i)
#define per(i, a, b) for (int i = (a); i >= (b); --i)

inline void work() {
    int n = rd();
    vector<int> cnt1(n, 0), cnt2(n, 0);
    rep(i, 0, n - 1) rep(j, 0, n - 1) {
        int w = i * j;
        ++cnt2[w % n];
        w = w / n;
        if (w) ++cnt1[w];
    }
    map<pii, vector<int>> f;
    rep(i, 0, n - 1) f[{cnt1[i], cnt2[i]}].push_back(i);

    map<char, int> c1, c2;
    set<char> ch;
    char s[20];
    rep(i, 1, n * n) {
        scanf("%s", s + 1);
        int l = strlen(s + 1);
        if (l == 1) {++c2[s[1]]; ch.insert(s[1]);}
        else {
            ++c1[s[1]]; ch.insert(s[1]);
            ++c2[s[2]]; ch.insert(s[2]);
        }
    }
    vector<char> ans(n);
    for (auto x : ch) {
        pii c = make_pair(c1[x], c2[x]);
        ans[f[c].back()] = x; f[c].pop_back();
    }
    rep(i, 0, n - 1) putchar(ans[i]); puts("");
}

int main() {
    per(t, rd(), 1) work();
    return 0;
}