public static long longLargestPrimeFactor()
{
long number = 600851475143;
long lastPrime = 1;
long largestPrimeNumber = 0;
while (lastPrime <= Math.Sqrt(number))
{
if (number % lastPrime == 0 && lastPrime > largestPrimeNumber)
{
largestPrimeNumber = lastPrime;
}
lastPrime = PrimeHelpers.GetNextPrime(lastPrime);
}
return(largestPrimeNumber);
}
public static long TruncatablePrimes()
{
long result = 0;
int count = 0;
long primeNumber = 11;
while (count < 11)
{
bool isFound = true;
long left = primeNumber;
long right = primeNumber;
int length = MathHelpers.IntLength(left);
while (length > 1)
{
length--;
left /= 10;
long rightPow = (long)Math.Pow(10, MathHelpers.IntLength(right) - 1);
long digit = right / rightPow;
right -= digit * rightPow;
if (!PrimeHelpers.IsPrimeNumber(left) || !PrimeHelpers.IsPrimeNumber(right))
{
isFound = false;
break;
}
}
if (isFound)
{
result += primeNumber;
count++;
}
primeNumber = PrimeHelpers.GetNextPrime(primeNumber);
}
return(result);
}
