91. Find the smallest natural number that, when divided by $4, 5, 6$, and 12, gives a remainder that is two units less than the divisor each time.
91. From the condition of the problem, it follows that if 2 is added to the required number, then it will be divisible by each of the given numbers. This means that the required number is equal to the least common multiple of the given numbers, decreased by 2. Answer. 58.