Fastest way do a spiral stair.

 From:  BurrMan
11084.8 In reply to 11084.3 
You could do the stairs and vertical step to generate the step count and footing by math,
Then boolean diff a slanted cone out to achieve the side shift of the steps. Then boolean diff and offset of the circle that encompasses the steps from the center of the array to get a nice symmetrical step sequence for the staircase to shift over