Find the sum of all positive integers a=2^{n} 3^{m}, where n and m are non-negative integers, for which a^{6} is not a divisor of 6^{a}.
Find the sum of all positive integers a=2^{n} 3^{m}, where n and m are non-negative integers, for which a^{6} is not a divisor of 6^{a}.