from collections import defaultdict
import itertools


for t in range(int(input())):
	N = int(input())
	S = input().split()

	buckets = defaultdict(list)

	cf = [0]*N
	cs = [0]*N

	for i in range(N):
		for j in range(N):
			hi = (i*j)//N
			lo = (i*j)%N
			cf[hi] += 1
			cs[lo] += 1

	for i in range(N):
		buckets[(cf[i], cs[i])].append(i)

	z = None
	for s in S:
		if S.count(s) == 2*N-1:
			z = s
			break

	cfs = defaultdict(int)
	css = defaultdict(int)
	sbux = defaultdict(list)

	S2 = []

	for s in S:
		if len(s) == 1:
			s = z + s
		S2.append(s)
		cfs[s[0]] += 1
		css[s[1]] += 1
	S2 = sorted(S2)

	for k in css:
		sbux[(cfs[k], css[k])].append(k)
	#print(sbux, buckets)
	for k in sbux:
		assert len(sbux[k]) == len(buckets[k])

	S = sorted(S)


	dfs_map = {}
	def dfs(order, i):
		if i == len(order):

			SC = []
			for x in range(N):
				for y in range(N):
					hi = (x*y)//N
					lo = (x*y)%N
					SC.append(dfs_map[hi] + dfs_map[lo])
			if sorted(SC) == S2:
				return True

		for p in itertools.permutations(sbux[order[i]]):
			for j in range(len(p)):
				dfs_map[buckets[order[i]][j]] = p[j]
			if dfs(order, i+1):
				return True


	dfs(sorted(sbux.keys()), 0)

	out = [None] * N
	for idx in dfs_map:
		out[idx] = dfs_map[idx]

	print("".join(out))