You have all the triads in mesa_boogie_man's link:

3 4 5

5 12 13

7 24 25

11 - 60 - 61

13 - 84 - 85

15 - 112 - 113

17 - 144 - 145

19 - 180 - 181

Big Job got it right too. Anyway, the numbers are a2 = b2 + c2 and the difference between b and c is just 1, so c=b+1. That gives you a2 = b2 + (b+1)2, therefore a2 = 2b2 + 2b + 1. You have "a", so just substitute and solve for b (like Drew said) What you are doing here is finding the Pythagorean triads in which c = b+1 and which correspond to the given 'a'

Now, you can be a smartass and give both solutions for each equation (the positive and the negative integers)

Geometrically it makes no sense, but it is algebraically correct

I wonder the point of this exercise. It doesn't exactly teach you much, does it? Oh yes, I know: find the solution on the internet, then work backwards and find the reason why LOL