The pattern in the given sequence is not immediately obvious. However, if we look closely, we can see that each number is obtained by multiplying the digits of the previous number. For example, 12 is obtained by multiplying 1 and 2, which gives us 2. Similarly, 36 is obtained by multiplying 3 and 6, which gives us 18. Following this pattern, the next number would be obtained by multiplying 2 and 4, which gives us 8. Therefore, the missing number is 8. However, the given answer is 64, which does not fit the pattern. Therefore, the correct answer is 8.