Fredholl numbers are numbers, which have 2 different digits, equal number of each one, and zero cannot be the first digit.
6-digit fredholl numbers are all composite because, all of them can be divided by 3.
Let's prove it:
Number can be divided by 3, when sum of it's digits can be divided by 3.
6-digit fredholl number must consist of three digits A, and three digits B.
So a sum of their digits is 3A+3B
3A+3B=3(A+B) so this number is divisible by 3,
Therefore any 6-digit fredholl number is divisible by 3.
