The number will be 3.
A square number is the result when a number has been multiplied by itself.
Let t number be x
So,
x = x² - 6
x² - x - 6=0
x² -3x + 2x -6 =0
x(x-3) + 2 (x-3) = 0
(x + 2)(x-3)=0
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