I don't know the answer I'm just answering some thing so that Brinley will let me ask a question. Hope this helps LOL
Answer:
look at the picture .................
Answer:

Step-by-step explanation:
We are given that a number 18234
We have to find the prime factorization of the number
Prime factorization : The number written is in the product of prime numbers is called prime factorization.
In order to find the prime factorization we will find the factors of given number

Hence, the prime factorization of 
As we can see that common difference is increasing to one more digit after every term
so it means
a21 = 231