Prime factorization is when you break down the factors of 31 to just the prime factors and expressing 31 as a product of those prime factors.
In this case, because 31 is a prime number, we can simply state the primary factorization as 31.
For most numbers, we would take the smallest prime factor that is larger than 1 to start to break down the focus number. In this case, the smallest prime factor larger than 1 is 31.
31 ÷ 31 = 1
If we divide 31 by 31, we simply get 1, which can’t be broken down any further.
So, the prime factorization of 31 is just 31.