From Reddit:

Write a program to calculate the Dottie number. This is the number you get when you type any number into a scientific calculator and then repeatedly press the

`cos`

button, with the calculator set to radians. The number displayed updates, getting closer and closer to a certain number, and eventually stops changing.

`cos`

here is the trigonometric function cosine, but you don’t need to know any trigonometry, or what cosine means, for this challenge. Just do the same thing you would with a handheld calculator: take cosine over and over again until you get the answer.

My solution is below the fold (I didn’t do optional challenge #3, mostly because real work had to be done before I got to it).