Bluebulb Projects' The Measure of Things presents:
3,900 is about one-and-four-fifths times the number of Steps in the Sears Tower.
In other words, it's 1.849 times the count of Steps in the Sears Tower, and the count of Steps in the Sears Tower is 0.5408 times that amount.
(a.k.a. Willis Tower) (Chicago, Illinois) (steps per stairwell)