3. Determine all pairs of natural numbers \(a\) and \(b\) for which

\[
2[a, b] + 3(a, b) = a b
\]

where \([a, b]\) denotes the least common multiple and \((a, b)\) denotes the greatest common divisor of the natural numbers \(a\) and \(b\).

(Jaroslav Švrček)