The number of feared Pythagoreans
1) I am not certain why you think they were feared: Greek history gives us no evidence of this.
2) I am not certain what you mean by number: They had a fundamental belief in "magic"and meaning in positive whole numbers.
http://www.dartmouth.edu/~matc/math5.geometry/unit3/unit3.html#Number Symbolism
You may be refering to the number ten, which Pythagoreans held in almost a religious reverence.