public static int[] CircularPrimesBelow(int l)
{
HashSet <int> circularPrimes = new HashSet <int>();
var primes = new SievePrimeNumberGenerator()
.GetPrimesBelowIntMaxValue()
.TakeWhile(p => p < l)
.ToList();
foreach (var prime in primes)
{
if (!circularPrimes.Contains(prime))
{
var rotations = prime.GetAllRotations();
if (AllRotationsArePrime(primes, rotations))
{
foreach (var rotation in rotations)
{
circularPrimes.Add(rotation);
}
}
}
}
return(circularPrimes.ToArray());
}
static void Main(string[] args)
{
// we know we only need 4 digit primes
var primes = new SievePrimeNumberGenerator().GetPrimesBelowIntMaxValue().SkipWhile(p => p < 1000).TakeWhile(p => p <= 9999).ToList();
// get all combinations where the primes form an arithmetic sequence
var sequences = from p1 in primes
from p2 in primes
from p3 in primes
where p1 < p2 && p2 < p3
where p2 - p1 == p3 - p2
select new
{
p1 = p1.ToString(),
p2 = p2.ToString(),
p3 = p3.ToString()
};
// filter to only the sequences that are permutations of each other
var perms = from tuple in sequences
where tuple.p1.GeneratePermutations().Contains(tuple.p2)
where tuple.p2.GeneratePermutations().Contains(tuple.p3)
select tuple.p1 + tuple.p2 + tuple.p3;
// find the only sequence which isn't the known one
var ans = perms.First(p => p != knownSequence);
Console.WriteLine(ans);
Console.WriteLine("Finished");
Console.ReadKey();
}
static void Main(string[] args)
{
var answer = new SievePrimeNumberGenerator().GetPrimesBelowLongMaxValue()
.Take(10001)
.ToList();
Console.WriteLine(answer.Last());
Console.ReadKey();
}
static void Main(string[] args)
{
var primes = new SievePrimeNumberGenerator().GetPrimesBelowLongMaxValue()
.TakeWhile(p => p < 2000000)
.ToList();
var sum = primes.Sum();
Console.WriteLine(sum);
Console.ReadKey();
}
static void Main(string[] args)
{
int upperBound = 1000000;
int[] nums = new int[upperBound];
var primes = new SievePrimeNumberGenerator().GetPrimesBelowIntMaxValue().TakeWhile(p => p <= upperBound);
// for each multiple of a prime, increment it's count by 1 (we found another prime divisor of it)
foreach (var prime in primes)
{
var num = prime + prime;
while (num < nums.Length)
{
nums[num]++;
num += prime;
}
}
// find the first set of 4 4s
int start = 0, count = 0;
for (int i = 0; i < nums.Length; i++)
{
if (nums[i] == 4)
{
count++;
if (count == 1)
{
start = i;
}
else if (count == 4)
{
Console.WriteLine(start);
break;
}
}
else
{
start = 0;
count = 0;
}
}
Console.ReadKey();
}
public static void Main(String[] args)
{
var primes = new SievePrimeNumberGenerator().GetPrimesBelowIntMaxValue().TakeWhile(p => p <= 1000000).ToArray();
for (int i = 2; i < primes.Length; i++)
{
for (int start = 0; start < primes.Length - i; start++)
{
int[] digits = new int[i];
for (int offset = 0; offset < i; offset++)
{
digits[offset] = primes[start + offset];
}
int sumOfDigits = 0;
try
{
sumOfDigits = digits.Sum();
}
catch (ArithmeticException)
{
// number overflowed what int could handle, clearly not < 1 million
continue;
}
if (sumOfDigits >= 1000000)
{
break;
}
else if (primes.Contains(sumOfDigits))
{
Console.WriteLine("{0}: {1}", i, sumOfDigits);
break;
}
}
}
Console.WriteLine("Finished");
Console.ReadKey();
}
static void Main(string[] args)
{
Stopwatch s = Stopwatch.StartNew();
var primes = new SievePrimeNumberGenerator().GetPrimesBelowLongMaxValue().TakeWhile(p => p <= 98765432).Reverse();
foreach (var prime in primes)
{
var primeStr = prime.ToString();
if (primeStr.IsPandigital(primeStr.Length))
{
Console.WriteLine(prime);
break;
}
}
s.Stop();
Console.WriteLine(s.Elapsed);
Console.ReadKey();
}
public override void SetUp()
{
generator = new SievePrimeNumberGenerator();
}