import itertools as it
n = 3
numbers = range(1, n + 1)
allValidSeries = (p for p in it.permutations(it.product(numbers, repeat=2)) if all(prev[1] == next[0] for prev, next in zip(p, p[1:])))
for t in enumerate(allValidSeries, 1):
	print("{0:3}. {1}".format(*t))