// Gives 76576500 and takes 1.3 seconds
public static double FirstRun()
{
const int divisorCount = 1000;
double value = 0;
double previousTriangleMax = 0;
var divisors = new HashSet <double>();
var maxDivisors = new HashSet <double>();
while (true)
{
previousTriangleMax++;
value += previousTriangleMax;
divisors.Clear();
// Skip if not divisible by 2
if (Math.Abs(value % 10) > double.Epsilon)
{
continue;
}
divisors.Add(1);
divisors.Add(value);
// Get all primes less than value
var root = Math.Sqrt(value);
//If sqrt is whole add to divisors
if (Math.Abs(Math.Floor(root) - root) < double.Epsilon)
{
divisors.Add(root);
}
var primes = PrimeHelper.GetAllPrimesLessThanValue(Math.Ceiling(root));
foreach (var prime in primes)
{
for (var i = prime; i <= root; i += prime)
{
if (!(Math.Abs(value % i) < double.Epsilon))
{
continue;
}
divisors.Add(i);
divisors.Add(value / i);
}
}
if (divisors.Count > maxDivisors.Count)
{
var array = new double[divisors.Count];
divisors.CopyTo(array);
maxDivisors = array.ToHashSet();
}
if (divisors.Count >= divisorCount)
{
return(value);
}
}
}