LCM( 1, 3 ) = 3
The formula for finding LCM is
$$ \text{LCM} (a, b) = \frac{ a \cdot b }{ \text{GCD}(a,b)} $$In this example we have: a = 1, b = 3 and GCD(1, 3) = 1.
$$ \text{LCM} (1, 3) = \frac{ 1 \cdot 3 }{ \text{GCD}(1,3)} = \frac{ 3 }{ 1 } = 3 $$