Its divisors ( other than the number itself : 6 ) are 1 , 2 , and 3 and 1 + 2 + 3 equals 6 . For example , the digital root of 8128 = 1 , since 8 + 1 + 2 + 8 = 19 , 1 + 9 = 10 , and 1 + 0 = 1 . The reason that this digital root does n't work with the perfect number 6 is because it only works with perfect numbers 2p â ' 1 ( 2p â ' 1 ) , with odd prime p ; the perfect number 6 being associated with the even prime 2 .