problems 02,03,04,05,06,07 done in C#

C#/02.EvenFiboNumbers.cs

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+// Project Euler : Problem Number02
+using System;
+namespace _2._Even_Fibonacci_numbers
+{
+    class EvenFiboNumbers
+    {
+        static int evenFibSum(int limit)
+        {
+            if (limit < 2)
+                return 0;
+
+            // Initialize first two even 
+            // prime numbers and their sum 
+            long ef1 = 0, ef2 = 2;
+            long sum = ef1 + ef2;
+
+            // calculating sum of even  
+            // Fibonacci value 
+            while (ef2 <= limit)
+            {
+
+                // get next even value of  
+                // Fibonacci sequence 
+                long ef3 = 4 * ef2 + ef1;
+
+                // If we go beyond limit, 
+                // we break loop 
+                if (ef3 > limit)
+                    break;
+
+                // Move to next even number 
+                // and update sum 
+                ef1 = ef2;
+                ef2 = ef3;
+                sum += ef2;
+            }
+
+            return (int)sum;
+        }
+
+        // Driver code 
+        public static void Main()
+        {
+            int limit = 4000000;
+            Console.Write(evenFibSum(limit));
+
+        }
+    }
+}

C#/03.largest_prime_fac.cs

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+//Euler problem03
+using System;
+namespace largest_prime_fac
+{
+    class largest_prime_fac
+    {
+        public static void Main()
+        {
+            long num = 600851475143;
+            int count = 3;
+            while (num > 1)
+            {
+                if (num % count == 0)
+                {
+                    num /= count;
+                }
+                else
+                {
+                    count += 2;
+                }
+            }
+            Console.WriteLine("The largest prime factor of the number {0} is {1} ", 600851475143, count);
+            Console.ReadKey();
+        }
+    }
+}

C#/04.Largest_palindrome_product

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+//Euler problem04
+using System;
+namespace _Largest_palindrome_product
+{
+    class Largest_palindrome_product
+    {
+        public static void Main()
+        {
+            for (int i = 999; i >= 100; i--)
+            {
+                for (int j = 999; j >= 100; j--)
+                {
+                    if (isPalindome(i * j) == true)
+                    {
+                        Console.WriteLine("Digit1: " + i);
+                        Console.WriteLine("Digit2: " + j);
+                        Console.WriteLine("Outcome: " + i * j);
+                        Console.ReadLine();
+                    }
+                }
+
+            }
+            Console.ReadLine();
+        }
+        public static bool isPalindome(int num)
+        {
+            string sNum = num.ToString();
+            for (int i = 0; i < sNum.Length / 2; i++)
+                if (sNum[i] != sNum[sNum.Length - 1 - i]) return false;
+
+            return true;
+        }
+    }
+}

C#/05.Smallest_multiple.cs

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+//Euler problem05
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace _Smallest_multiple
+{
+    class Smallest_multiple
+    {
+        public static void Main()
+        {
+            Console.WriteLine(Calc(20));
+        }
+        static List<int> Factors(int n)
+        {
+            List<int> list = new List<int>();
+            int i = 2;
+            while (i <= n)
+            {
+                if (n % i == 0)
+                {
+                    list.Add(i);
+                    n /= i;
+                }
+                else
+                    i++;
+            }
+            return list;
+        }
+
+        static int Calc(int n)
+        {
+            var factors = Enumerable.Range(2, n - 1).Select(j => Factors(j)).ToList();
+
+            int i = 2;
+            int res = 1;
+            while (i <= n)
+            {
+                if (factors.Count(l => l.Contains(i)) > 1)
+                {
+                    factors.ForEach(l => l.Remove(i));
+                    res *= i;
+                }
+                else
+                    i++;
+            }
+
+            return res * factors.SelectMany(x => x).Aggregate((s, j) => s *= j);
+        }
+    }
+}

C#/06.Sum_square_difference

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+//Euler problem06
+using System;
+
+public class Sum_square_difference
+{
+	public static void Main()
+	{
+				int n=10;
+		//sum of square first 100numbers
+		//1^2+2^2+3^2....
+		long sum1=(n*(n+1)*(2*n+1))/6;
+		//sum of first 100 numbers square
+		//(1+2+3...)^2
+		long sum2=((n*(n+1))/2)*((n*(n+1))/2);
+		Console.WriteLine(sum2-sum1);
+	}
+}

C#/07.Prime_10001st.cs

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+//Euler problem07
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace _Prime_10001st
+{
+    class Prime_10001st
+    {
+        public static void Main()
+        {
+            List<long> primeNumbers = new List<long>() { 2 };
+            for (long i = 3; i < long.MaxValue; i += 2)
+            {
+                if (!primeNumbers.Any(p => (i % p) == 0))
+                {
+                    primeNumbers.Add(i);
+                    if (primeNumbers.Count == 10001)
+                    {
+                        Console.WriteLine(i);
+                        break;
+                    }
+                }
+            }
+        }
+    }
+}