This can be found/proven by replacing "n" with term number (1,2,3,4...), then solving to get the final number. For example 3 * 1^2 + 2. You would first do 1^2, which is 1. Next, you would multiply 1 by 3, to get 3. Finally, you'd and the 2 to get 5. 5 is the 1st term, and you can use this same equation to get the rest of the terms you need.
Because each integer can be written as n/1 and integers can be positive and negative. For example, 3= 3/1 , 3 is the rational number. But all rational numbers like 1/2 =0.5 are not an integer. (fractions, decimals are not integers.)
