FindPrimesNoFilter.cs

private static IEnumerable<int> FindFirstNumPrimes( int limit )
    {
      List<int> primes = new List<int>( new[] { 2 } );
      bool isPrime;
      int i = 1;

      while( primes.Count < limit )
      {
        i += 2;
        isPrime = true;

        foreach( int prime in primes )
        {
          if( i % prime == 0 )
          {
            isPrime = false;
            break;
          }
        }

        if( isPrime )
          primes.Add( i );
      }
      return primes;
    }

FindPrimesWithFilter.cs

private static IEnumerable<int> FindFirstNumPrimesFilter( int limit )
    {
      List<int> primes = new List<int>( new[] { 2 } );
      IEnumerable<int> tprimeList;
      bool isPrime;
      int i = 1;

      while( primes.Count < limit )
      {
        i += 2;
        isPrime = true;
        double sqrtI = Math.Sqrt( i );

        if ( sqrtI == Math.Floor( sqrtI ) && primes.Contains( (int)sqrtI ) )
          continue;

        tprimeList = primes.Where( j => j < sqrtI );

        foreach( int prime in tprimeList )
        {
          if( i % prime == 0 )
          {
            isPrime = false;
            break;
          }
        }

        if( isPrime )
          primes.Add( i );
      }

      return primes;
    }