n % x == 0
Means that n can be divided by x. So... for instance, in your case:
boolean isDivisibleBy20 = number % 20 == 0;
Also, if you want to check whether a number is even or odd (whether it is divisible by 2 or not), you can use a bitwise operator:
boolean even = (number & 1) == 0;
boolean odd = (number & 1) != 0;