These are not differences.
17 = 4^2 + 1^2
16 = 2^2 * 2^2
20 = 4^2 + 2^2
18 = 3^2 + 3^2
15 can be written as the difference between two positive perfect squares:
15=4²-1²=16-1
Which of the following numbers cannot be written as the difference of two positive perfect squares?
16
17
18
19
20
1 answer