In order for each level to exclude numbers that have already been counted, each level would only be 9 numbers: So if level = lambda n: 1-int(math.log10(1./n))

In order for each level to exclude numbers that have already been counted, each level would only be 9 numbers: So if level = lambda n: 1-int(math.log10(1./n)) We only ever generate [‘.’ + ‘0’ * (level(n) – 1) + str(i + 1) for i in range(9)]