Absolute Apparent Brightness
Relative Apparent Brightness
The value for the luminosity (L) will be 1.0, since the Sun is the standard candle for this equation. The value for the distance (D) is the distance from the Sun to Mars  in Astronomical Units, or ~1.524 AU.
The equation works out as:
Kalvéru is 1.618 times as bright as the Sun at any particular distance, but this little bit of knowledge can be a dangerous thing. Finding Kalvéru's apparent brightness this way means that one must always remember to calculate the apparent brightness of the Sun at a given distance and then multiply that result by the luminosity of the star in solar units (in this case, 1.618) to get the relative apparent brightness of Kalvéru compared to the Sun.
The safer route is just to calculate the apparent brightness directly.
So, if Kalvéru has a planet (Dynón) orbiting at Mars' distance from the Sun (1.524 AU), how bright does Kalvéru appear to inhabitants of Dynón?
Setting L = 1.618 and D = 1.524, the equation tells us:
If we divide the result for Dynón by the result for Mars:
But, since Kalvéru's planets aren't likely to be at exactly the same orbital distances as are the Solar System planets from the Sun, the apparent brightness for any and each of Kalvéru's planets needs to be calculated independently.