Add a solution to the problem 72
Use a sieving approach
Move pdf-files to doc
Add a solution to the problem 73
Use a faster algorithm
Transform the recursion into a loop
Use int instead of float
Add *.out and *.so to .gitignore
Minor changes
Rewrite the is_prime function in C
Add a solution to the problem 74
Hardcode the factorials
Minor changes
Add a solution to the problem 75
Use a faster algorithm
Replace range with xrange
Use new-style classes
Improve the readability/performance
Add a solution to the problem 76 (by analogy with the problem 31)
Same algorithm, but more compact