Task: Mersenne primes
C#: using System;
using System.Numerics;

namespace MersennePrimes {
    class Program {
        static BigInteger Sqrt(BigInteger x) {
            if (x < 0) throw new ArgumentException("Negative argument.");
            if (x < 2) return x;
            BigInteger y = x / 2;
            while (y > x / y) {
                y = ((x / y) + y) / 2;
            }
            return y;
        }

        static bool IsPrime(BigInteger bi) {
            if (bi < 2) return false;
            if (bi % 2 == 0) return bi == 2;
            if (bi % 3 == 0) return bi == 3;
            if (bi % 5 == 0) return bi == 5;
            if (bi % 7 == 0) return bi == 7;
            if (bi % 11 == 0) return bi == 11;
            if (bi % 13 == 0) return bi == 13;
            if (bi % 17 == 0) return bi == 17;
            if (bi % 19 == 0) return bi == 19;

            BigInteger limit = Sqrt(bi);
            BigInteger test = 23;
            while (test < limit) {
                if (bi % test == 0) return false;
                test += 2;
                if (bi % test == 0) return false;
                test += 4;
            }

            return true;
        }

        static void Main(string[] args) {
            const int MAX = 9;

            int pow = 2;
            int count = 0;

            while (true) {
                if (IsPrime(pow)) {
                    BigInteger p = BigInteger.Pow(2, pow) - 1;
                    if (IsPrime(p)) {
                        Console.WriteLine("2 ^ {0} - 1", pow);
                        if (++count >= MAX) {
                            break;
                        }
                    }
                }
                pow++;
            }
        }
    }
}

Python: import random


def MillerRabinPrimalityTest(number):
    
    if number == 2:
        return True
    elif number == 1 or number % 2 == 0:
        return False
    
    
    
    
    oddPartOfNumber = number - 1
    
    
    timesTwoDividNumber = 0
    
    
    while oddPartOfNumber % 2 == 0:
        oddPartOfNumber = oddPartOfNumber / 2
        timesTwoDividNumber = timesTwoDividNumber + 1 
     
    
    for time in range(3):
        
        
        while True:
            
            randomNumber = random.randint(2, number)-1
            if randomNumber != 0 and randomNumber != 1:
                break
        
        
        randomNumberWithPower = pow(randomNumber, oddPartOfNumber, number)
        
        
        if (randomNumberWithPower != 1) and (randomNumberWithPower != number - 1):
            
            iterationNumber = 1
            
            
            while (iterationNumber <= timesTwoDividNumber - 1) and (randomNumberWithPower != number - 1):
                
                randomNumberWithPower = pow(randomNumberWithPower, 2, number)
                
                
                iterationNumber = iterationNumber + 1
            
            if (randomNumberWithPower != (number - 1)):
                return False
            
    
    return True


MAX = 20
p = 2
count = 0
while True:
    m = (2 << (p - 1)) - 1
    if MillerRabinPrimalityTest(m):
        print "2 ^ {} - 1".format(p)
        count = count + 1
        if count == MAX:
            break
    
    while True:
        p = p + 2 if (p > 2) else 3
        if MillerRabinPrimalityTest(p):
            break
print "done"