Here you are a brief explanation of all controls in Nuke's random expression.
This is the full function 'by default':
or just simplified: random(1,frame)
This creates a curve containing random values between 0 and 1.
The breakdown controls:
seed value randomly changes the curve without modify its nature
frequency value increase or reduce the amount of oscillations (1 = 1 peak per frame by default)
amplitude indicates the maximum value of your oscillation (max=1 by default)
valueOffset value decides where the curve sits on Y axis (0 by default)
if you want to generate a curve with random values between 2 and 8 with a (low) frequency of 1 peak every 5 frames this is the formula:
You can use this function as an expression in any numerical knob.