I have a program that calculates N digits of Pi.
I have measured that it takes 10x time to calculate 3n numbers, compared with the time for calculating n numbers. The source code also gives an indication for this running times.
For example, if 1000 digits take 0.011 seconds, 3000 digits take 0.11 seconds, and 9000 digits take 1.1 seconds.
What is the Big O complexity of such algorithm?
Here's the source code.