Brain-Games is a series of mathematical games.
brain-even. The user should answer "yes" if the number is even, otherwise answer "no".
brain-calc. The user should evaluate the result of the expression.
brain-gcd. The user should find the greatest common divisor of given numbers.
brain-progression. The user should define the number is missing in the progression.
brain-prime. The user should answer "yes" if given number is prime, otherwise answer "no".
