Of all the natural numbers from 1 to 400, those numbers have only three divisors
4. 9, 25, 49, 121, 169 prime number square, 19 * 19 = 381
7. The sum of the greatest common divisor and the second greatest common divisor of a natural number is 111. What is the natural number?
A number has no common divisor
If 3 ^ m + n is divisible by 13, then 3 ^ m + N + 3 is divisible by 13
3 ^ m + N + 3 square = 3 ^ 3 * (3 ^ m + n square) because 3 ^ m + n square can be divided by 13, it is as the title says