For all the the integers in the interval [300, 800] which are a multiple of 18, find for each number the amount of iterations required to reach 1, as if the number was used to start the sequence in the Collatz conjecture. The solution to the challenge is the sum of all the resulting numbers.
The Collatz conjecture concerns a sequence that starts with any positive number n. Each next term is obtained using the following rules: If n is even, divide it by 2. If n is odd, multiply it by 3 and add 1. The conjecture states that repeating this process will result in the sequence converging to the number 1. For example the number 13 requires 9 iterations to reach 1, namely: [40, 20, 10, 5, 16, 8, 4, 2, 1].