Day1

using System;
using System.Collections.Generic;

namespace Day1
{
    class Program
    {
        static bool IsPrime(int number)
        {
            for (int i = 2; i*i <= number; i++)
            {
                if (number % i == 0)
                {
                    return false;
                }
            }
            return true;
        }
        static List<int> Factorisation(int number)
        {
            List<int> factors = new List<int>();
            for (int i = 2; i*i <= number; i++)
            {
                while (number % i == 0)
                {
                    factors.Add(i);
                    number /= i;
                }
            }
            if (number > 1)
            {
                factors.Add(number);
            }
            return factors;
        }

        static List<int> EratosthenesPrimes(int n)
        {
            List<int> primes = new List<int>();
            int[] arr = new int[n + 1];
            for (int i = 2; i <= n; i++)
            {

                if (arr[i] == 0)
                {
                    primes.Add(i);
                    for (int j = 2*i; j <= n; j += i)
                    {
                        arr[j] = 1;
                    }
                }
            }
            return primes;
        }
        static void Main(string[] args)
        {
            Console.Write("Enter number: ");
            int num = int.Parse(Console.ReadLine());
            //int num = 200;
            Console.WriteLine("Is prime({0}): {1}", num, IsPrime(num));
            Console.WriteLine("{0} = {1}", num, string.Join("*", Factorisation(num)));
            Console.WriteLine("Primes to {0}: {1}", num, string.Join(", ", EratosthenesPrimes(num)));
        }
    }
}