Maths functions and experimentation (Fibonacci, Mersenne Primes etc)

Maths.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace Maths
{
  internal class Maths
  {
    public static IEnumerable<long> Fibonacci(int n)
    {
      for (long i = 0, previousFib = 0, currentFib = 1; i < n; i++)
      {
        yield return previousFib;
        long result = previousFib + currentFib;
        previousFib = currentFib;
        currentFib = result;
      }
    }

    public static IEnumerable<long> Primes(int n)
    {
      int val = 2;

      for (int i = 0; i < n; )
      {
        if (IsPrime(val))
        {
          i++;
          yield return (val++);
        }
        else
        {
          val++;
        }
      }
    }

    public static bool IsPrime(long n)
    {
      if (n < 2 || (n % 2 == 0 && n != 2)) return false;
      if (n == 2 || n == 3) return true;

      double sqrt = Math.Sqrt(n);
      long limit = Convert.ToInt64(Math.Floor(sqrt));

      for (int i = 3; i <= limit; i++)
        if (n % i == 0) return false;

      return true;
    }

    public static IEnumerable<long> Mersennes(int n)
    {
      for (int i = 0; i < n; i++)
        yield return Convert.ToInt64(Math.Pow(2.0, i)) - 1;
    }

    public static List<int> Factors(int n)
    {
      List<int> factors = new List<int>();

      for (int i = 1; i <= n; i++)
        if (n % i == 0) factors.Add(i);

      return factors;
    }

    public static IEnumerable<long> Perfects(int limit)
    {
      int i = 2;
      int found = 0;

      while (found < limit)
      {
        if (IsPerfect(i))
        {
          yield return i;
          found++;
        }

        i++;
      }
    }

    public static Boolean IsPerfect(int n)
    {
      List<int> factors = Factors(n);

      if (factors.Count > 2)
      {
        factors.RemoveAt(factors.Count - 1);

        int sum = factors.Aggregate((x, y) => x + y);

        if (sum == n) return true;
      }

      return false;
    }
  }
}