How to generate numbers upto 18 digits, sum of whose reciprocals is a whole number : <p>I am looking for a way to generate a series of numbers whose sum of reciprocals is a whole number? </p>

<p>For eg - 11  (1/1 + 1/1 = 2 is a whole number), 122 (1/1+1/2+1/2 is a whole number), 236 (1/2 + 1/3 + 1/6 is a whole number)
and likewise.</p>

<p>Also I want to avoid repeat of same combination or permutation of digits. For example, if 122 is printed, I don't want to print 212 and 221.</p>

<p>I want to know how to approach this problem </p>
