# your code goes hereimport sys
import math
 
primes = []
 
def gcd(a, b):
    if a == 0:
        return b
    return gcd(b % a, a)
 
if __name__ == "__main__":
    t = int(input())
    # print(gcd(10**100, 10**87), "<--")
    for t_ in range(1, t + 1):
        print("Case #", t_,": ", end = '', sep = '')
        n, l = [int(x) for x in input().strip().split(' ')]
        ar = [int(x) for x in input().strip().split(' ')]
        factors = []
        for i in range(l - 1):
            factors.append(gcd(ar[i + 1], ar[i]))
        factors = [ar[0] // factors[0]] + factors 
        factors = factors + [ar[-1] // factors[-1]]
        factors_ = list(set(factors))
        factors_.sort()
        for i in range(len(factors_)):
            if factors_[i] <= 1:
                del factors_[i]
                i -= 1
        my_dict = {}
 
        for i in range(26):
            my_dict[factors_[i]] = chr(ord('A') + i)
 
        # assert len(factors_) == 26
 
        # print(factors_)
 
        for i in factors:
            print(my_dict[i], end = '')
        print()
 
 

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