For the surd

$\displaystyle a_n = \sqrt{k + \sqrt{k + \sqrt{k + \sqrt{k + ....... \infty }}}} $

therefore

$\displaystyle x = ({1+\sqrt{1+4k}}){/2} $

The task is: What's a general statement which represents values for k which make the exact value an integer.

What does the question mean by 'general statement'? what form is my answer supposed to be in?