public override long Solve()
{
var bRange = Primes.CalculatePrimesBelow(MAX_COEFF);
var aRange = Enumerable.Range(-999, 1999);
long maxPrimesCount = 0;
long maxACoeff = 0;
long maxBCoeff = 0;
foreach (var b in bRange)
{
foreach (var a in aRange)
{
long n = 0;
while (Primes.IsPrime((n * n) + (a * n) + b))
{
n++;
}
if (n > maxPrimesCount)
{
maxPrimesCount = n;
maxACoeff = a;
maxBCoeff = b;
}
}
}
return(maxACoeff * maxBCoeff);
}
public override long Solve()
{
for (int i = 9; i > 0; i--)
{
var pandigitals = Pandigitals.Generate(i).OrderByDescending(p => p);
foreach (var pandigital in pandigitals)
{
if (Primes.IsPrime(pandigital))
{
return(pandigital);
}
}
}
return(0);
}
public static long LargestPrimeFactor(long number)
{
//start at sqrt of number.
var limit = (long)Math.Sqrt(number);
long largestPrimeFactor = 0;
for (long i = limit; i > 0; i--)
{
if (number % i == 0 && Primes.IsPrime(i))
{
largestPrimeFactor = i;
break;
}
}
return(largestPrimeFactor);
}
public override long Solve()
{
int currentCornerNumber = 1;
int sideLength = 1;
int spiral = 1;
while (RatioOfPrimes >= 0.1M || numberOfPrimes == 0)
{
for (int i = 1; i <= 4; i++)
{
var primetoCheck = currentCornerNumber += 2 * spiral;
if (Primes.IsPrime(primetoCheck))
{
numberOfPrimes++;
}
numberOfCornerNumbers++;
}
sideLength += 2;
spiral++;
}
return(sideLength);
}
public override long Solve()
{
for (int number = 1490; number < 9999; number++)
{
var perms = Permutations.Generate(number).Where(p => p.ToString().Length == 4);
var permsList = new List <long>();
perms.ToList().ForEach(p => { if (Primes.IsPrime(p))
{
permsList.Add(p);
}
});
if (permsList.Count >= 4)
{
var sequence = FindSequence(permsList);
if (sequence.Count > 0 && !sequence.Contains(1487))
{
return(long.Parse(sequence[0].ToString() + sequence[1].ToString() + sequence[2].ToString()));
}
}
}
throw new Exception("Cannot find sequence....you messed it up");
}
public override long Solve()
{
long smallestSum = 0;
var primes = Primes.CalculatePrimesBelow(10000);
foreach (var first in primes)
{
foreach (var second in primes)
{
if (second <= first)
{
continue;
}
if (Primes.IsPrime(Concat(first, second)) && Primes.IsPrime(Concat(second, first)))
{
foreach (var third in primes)
{
if (third <= second)
{
continue;
}
if (Primes.IsPrime(Concat(first, third)) && Primes.IsPrime(Concat(third, first)) &&
Primes.IsPrime(Concat(second, third)) && Primes.IsPrime(Concat(third, second)))
{
foreach (var fourth in primes)
{
if (fourth <= third)
{
continue;
}
if (Primes.IsPrime(Concat(first, fourth)) && Primes.IsPrime(Concat(fourth, first)) &&
Primes.IsPrime(Concat(second, fourth)) && Primes.IsPrime(Concat(fourth, second)) &&
Primes.IsPrime(Concat(third, fourth)) && Primes.IsPrime(Concat(fourth, third)))
{
foreach (var fifth in primes)
{
if (fifth <= fourth)
{
continue;
}
if (Primes.IsPrime(Concat(first, fifth)) && Primes.IsPrime(Concat(fifth, first)) &&
Primes.IsPrime(Concat(second, fifth)) && Primes.IsPrime(Concat(fifth, second)) &&
Primes.IsPrime(Concat(third, fifth)) && Primes.IsPrime(Concat(fifth, third)) &&
Primes.IsPrime(Concat(fourth, fifth)) && Primes.IsPrime(Concat(fifth, fourth)))
{
Console.WriteLine("1: {0} 2: {1} 3: {2} 4: {3} 5: {4}", first, second, third, fourth, fifth);
var sum = new List <long> {
first, second, third, fourth, fifth
}.Sum();
if (sum < smallestSum || smallestSum == 0)
{
smallestSum = sum;
}
}
}
}
}
}
}
}
}
}
return(smallestSum);
}
