This is the only non-square number in the group.
This is the only complete square in the group.
All others first and last two digits are same.
Except '64,73', all are having difference of 11.
In all others, 2nd number is 2 more than the first.
In all others, 2nd number = 1st number + 6
In all other, 2nd number = 1st number/3
In all other numbers the sum of the digits is 17.
All other pairs consists of prime number only.
In all other pairs, the difference between the two numbers is a multiple of 9.
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