Given two numbers a and b, and a number k which is odd. The task is to find all the numbers between a and b (both inclusive) having exactly k divisors.
Input : a = 2, b = 49, k = 3 Output: 4 // Between 2 and 49 there are four numbers // with three divisors // 4 (Divisors 1, 2, 4), 9 (Divisors 1, 3, 9), // 25 (Divisors 1, 5, 25} and 49 (1, 7 and 49) Input : a = 1, b = 100, k = 9 Output: 2 // between 1 and 100 there are 36 (1, 2, 3, 4, 6, 9, 12, 18, 36) // and 100 (1, 2, 4, 5, 10, 20, 25, 50, 100) having exactly 9 // divisors
This problem has simple solution, here we are given that k is odd and we know that only perfect square numbers have odd number of divisors , so we just need to check all perfect square numbers between a and b, and calculate divisors of only those perfect square numbers.
This problem can be solved more efficiently. Please refer method 2 of below post for an efficient solution.
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Improved By : nitin mittal