Each of P, Q, R, S and T are positive integers with P < Q < R < S < T. Determine the maximum value of the following expression.
[P, Q]^{ 1} + [Q, R]^{ 1} + [R, S]^{ 1} + [S, T]^{ 1}
Note: [x, y] represents the LCM of x and y.


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