Updated numerous Mathematica solutions.
P31: Added memoization, tweaked formatting.
P32: Renamed variable to be less similar to built-in function, removed print, improved output.
P53: Simplified code.
P66, P71: Improved output.
P121: Deleted extra semicolon.
P171: Added comment.
P381: Renamed variable, simplified code.
Improved Mathematica solutions.
P92: Added memoization to speed up by 4 times.
P104: Rewrote algorithm to fix memory exhaustion and decrease running time.