【正确答案】 1、53    

【答案解析】The best way to determine the prime factors of a large number is to use a factor tree. Start with 636, and divide by any available prime factor: for instance, two factors of 636 are 2 and 318. Next, 318 is divisible by the prime number 3, leaving 106. Finally, 106 is divisible by 2, which leaves you with 53.