SOLUTION: Hello, How would I solve the following problem: Find a counterexample to the statement: The square of a number added to the sum of three times the number and 7 is a prime n

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Question 291117: Hello,
How would I solve the following problem:
Find a counterexample to the statement: The square of a number added to the sum of three times the number and 7 is a prime number.Justify your solution by supporting it with step by step work

This is the answer I came up with not sure it right
If the number is n, then you mean the statement:
n^2 + 3n + 7 is prime
Let n = 3k where k is an integer, i.e. n is a multiple of 3.
Then the expression becomes
49k^2 + 21k + 3
= 3(7k^2 + 3k + 1)
I am not sure this is right but I did try please let me know thank you so much for your help.
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
One counter example is sufficient:
9^2 + 3*9 + 7 = 115 which is not prime.