public static int SpiralPrimes()
{
float rate = 100;
int spiralLength = 1;
int primeCount = 0;
int lastCorner = 1;
int loopCount = 0;
while (rate > 0.1)
{
loopCount++;
spiralLength += 2;
for (var i = 0; i < 4; i++)
{
lastCorner += (spiralLength - 1);
if (PrimeHelpers.IsPrimeNumber(lastCorner))
{
primeCount++;
}
}
rate = (float)primeCount / (float)((loopCount * 4) + 1);
}
return(spiralLength);
}
public static decimal PrimePermutations()
{
decimal result = 0;
int number = 1489;
int increasingNumber = 3330;
while (number <= 9999)
{
int n1 = number;
int n2 = n1 + increasingNumber;
int n3 = n2 + increasingNumber;
if (PrimeHelpers.IsPrimeNumber(n1) && PrimeHelpers.IsPrimeNumber(n2) && PrimeHelpers.IsPrimeNumber(n3))
{
if (MathHelpers.IsPermutation(n1, n2) && MathHelpers.IsPermutation(n1, n3))
{
result = MathHelpers.ConcatenateNumbers(new List <decimal> {
n1, n2, n3
});
break;
}
}
number++;
}
return(result);
}
public static long NextPrime(long number)
{
while (true)
{
if (PrimeHelpers.IsPrimeNumber(number))
{
return(number);
}
number++;
}
}
public static long SummationOfPrimes()
{
int number = 2000000;
long summartionPrimes = 0;
for (int i = 2; i < number; i++)
{
if (PrimeHelpers.IsPrimeNumber(i))
{
summartionPrimes += i;
}
}
return(summartionPrimes);
}
static bool IsCricularPrimes(int primeNumber)
{
int circularNumber = MathHelpers.GetNextCircularNumber(primeNumber);
while (circularNumber != primeNumber)
{
if (!PrimeHelpers.IsPrimeNumber(circularNumber))
{
return(false);
}
circularNumber = MathHelpers.GetNextCircularNumber(circularNumber);
}
return(true);
}
public static int Prime10001st()
{
int maxNumber = 10001;
int numberOfPrime = 1;
int prime = 1;
while (numberOfPrime <= maxNumber)
{
prime += 1;
if (PrimeHelpers.IsPrimeNumber(prime))
{
numberOfPrime += 1;
}
}
return(prime);
}
public static long CircularPrimes()
{
int circularPrimesCount = 0;
for (var i = 0; i < 1000000; i++)
{
if (PrimeHelpers.IsPrimeNumber(i))
{
if (IsCricularPrimes(i))
{
circularPrimesCount++;
}
}
}
return(circularPrimesCount);
}
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);
}
public static long QuadraticPrimes()
{
long result = 0;
int maxPrimeCount = 0;
for (int a = -1000; a <= 1000; a++)
{
for (int b = -1000; b <= 1000; b++)
{
int n = 0;
while (PrimeHelpers.IsPrimeNumber(Math.Abs(n * n + a * n + b)))
{
n++;
}
if (n > maxPrimeCount)
{
maxPrimeCount = n;
result = a * b;
}
}
}
return(result);
}