идеальное число

public static bool IsPerfectNumber(int number)
{
  if (number < 0)
  {
    throw new ArgumentException($"{nameof(number)} cannot be negative");
  }

  var sum = 0; /* sum of its positive divisors */
  for (var i = 1; i < number; ++i)
  {
    if (number % i == 0)
    {
      sum += i;
    }
  }

  return sum == number;
}
PrashantUnity