Prove that (2*a^2 + 7a + 3)/(a + 3) is an odd number for any positive integer number, a.

We see that the numerator is a quadratic, so we factorise it to obtain:

(2a + 1)(a + 3)/(a + 3) = 2a + 1

Since a is a positive integer, we know that 2*a + 1 will always be an odd number.