#define _CRT_SECURE_NO_DEPRECATE
#include<iostream>
#include<algorithm>
#include<cmath>
#include<vector>
#include<cstring>
#include<queue>
using namespace std;
#define INF 0x3f3f3f3f
#define EPS 1e-7
typedef unsigned long long ll;
const int N_MAX = 150000+10;
const int MOD = 1e10+7;
int n,st[N_MAX],t;//堆栈st保存当前一层所有的节点的下标
bool vis[N_MAX];
char a[N_MAX],ans[N_MAX],_max;
struct Node {
    int index, step;
    Node(int index = 0, int step = 0) :index(index), step(step) {}
    bool operator < (const Node &b)const {
        if (this->step != b.step)return step > b.step;
        else return a[this->index] < a[b.index];
    }
};

void init(int &n) {
    memset(st, 0, sizeof(n));
    t = 0;
    memset(vis, 0, sizeof(vis));
    for (int i = 0; i < n; i++)ans[i] = '0'-1;
    _max = '0'-1;
}

void bfs() {
    priority_queue<Node>que;
    for (int i = 0; i < n; i++) {
        if (_max == a[i]) { que.push(Node(i, 0));  }//初始将值最大的元素节点压入队列
    }
    int pre_step = -1,t=0;
    while (!que.empty()) {
        Node p = que.top(); que.pop();
        if (pre_step != p.step) {//判断当前是第几层，如果到达新一层，之前记录销毁
            pre_step = p.step;
            while (t)vis[st[--t]] = false;
        }
        if (ans[p.step] > a[p.index] || p.step >= n || vis[p.index])continue;//如果当前的节点value比较小或者当前节点已经走过，剪枝
        ans[p.step] = a[p.index];
        st[t++] = p.index;
        vis[p.index] = true;
        que.push(Node(((ll)p.index*p.index+1)%n,p.step+1));
    }
    
}



int main() {
    int t; scanf("%d",&t);
    for (int cs = 1; cs <= t;cs++) {
        scanf("%d", &n);
        init(n);
        scanf("%s",a);
        for (int i = 0; i < n;i++) _max = max(_max, a[i]);
        bfs();
        ans[n] = '\0';
        printf("Case #%d: %s\n",cs,ans);
    }
    return 0;
}