In 6-digit fredholl number, all numbers must consist of three digits A, and three digits B.
So a sum of their digits is 3A+3B
3A+3B=3(A+B) and this number is divisible by 3,
Therefore any 6-digit fredholl number is divisible by 3.
If a number is divisible by any other number than 1 and itself, we call that number a composite number.