The LCMs of \(6\) with \(5,10,15\) are each \(30\). For example, the multiples of \(15\) begin \(15,30\), and only \(30\) is a multiple of \(6\).

\(20\) does not divide \(30\), so \(30\) cannot be its common multiple with \(6\). In fact, their LCM is \(60\).

Answer

\(n=5,10,15\)