public long Problem3()
{
long number = 600851475143;
List <long> primes = new List <long>();
for (long i = 2; i <= Math.Pow(number, 0.5); i++)
{
if (number % i == 0)
{
long otherDivisor = number / i;
if (MathsHelper.IsPrime(i))
{
primes.Add(i);
}
else
{
if (MathsHelper.IsPrime(otherDivisor))
{
return(otherDivisor);
}
}
}
}
primes.Reverse();
return(primes[0]);
}
public void Problem27()
{
Dictionary <long, bool> isPrimeDict = new Dictionary <long, bool>();
long maxConsecutive = 0;
Tuple <long, long> coeffs;
for (long a = -500; a < 500; a++)
{
long aValue = (2 * a) + 1;
for (long b = -500; b < 500; b++)
{
long bValue = (2 * b) + 1;
//bool resultPrime = true;
while (true)
{
long quadValue = this.GetQuadraticValue(aValue, bValue, 0);
if (!isPrimeDict.ContainsKey(quadValue))
{
bool isPrime = MathsHelper.IsPrime(quadValue);
isPrimeDict.Add(quadValue, isPrime);
}
if (isPrimeDict[quadValue])
{
maxConsecutive++;
coeffs = Tuple.Create(aValue, bValue);
}
else
{
break;
}
}
}
}
}
public int TheNthPrimeIs(int whichNumerPrime)
{
int i = 1;
int numberToTest = 3;
while (i < whichNumerPrime)
{
if (MathsHelper.IsPrime(numberToTest))
{
i++;
}
numberToTest++;
}
return(numberToTest - 1);
}
public int Problem37()
{
var truncatable = new Dictionary <int, IEnumerable <IEnumerable <int> > >();
IEnumerable <IEnumerable <int> > choices = new int[][] { new int[] { 1 }, new int[] { 3 }, new int[] { 7 }, new int[] { 9 } };
var tailElements = new HashSet <int>(new int[] { 3, 7 });
//var primes = new HashSet<int>(GetPrimesUpTo(1000000000));
//primes.
Func <IEnumerable <int>, int> getNumber = list => list.Reverse().Select((i, j) => i * MathsHelper.Power(10, j)).Sum();
Func <IEnumerable <int>, IEnumerable <IEnumerable <int> > > getRLSubsets = list => list.Select((i, j) => list.Skip(j));
truncatable.Add(1, new int[][] { new int[] { 2 }, new int[] { 3 }, new int[] { 5 }, new int[] { 7 } });
for (int q = 2; q < 20; q++)
{
truncatable[q] = truncatable[q - 1].SelectMany(p => choices, (r, t) => r.Concat(t));
truncatable[q] = truncatable[q].Where(x => MathsHelper.IsPrime((long)getNumber(x))).ToList();
truncatable[q - 1] = truncatable[q - 1].Where(x => getRLSubsets(x).Select(getNumber).All(y => MathsHelper.IsPrime((long)y)));
if (truncatable[q - 1].Count() == 0)
{
truncatable[q] = new List <IEnumerable <int> >();
break;
}
}
var tyy = truncatable.Where(x => x.Key >= 2).Select(x => x.Value).Select(x => x.Select(getNumber)).SelectMany(x => x).Sum();
IEnumerable <int> test = Enumerable.Range(1, 4);
var hg = test.Select((i, j) => test.Skip(j));
return(0);
}