public static int PentagonNumbers(int n)
{
int min = int.MaxValue;
List <long> pentagons = SpecialSequences.pentagonalnumbers(n);
HashSet <long> hashpent = new HashSet <long>(pentagons);
foreach (int k in pentagons)
{
foreach (int j in pentagons)
{
int tempsum = k + j;
if (!hashpent.Contains(tempsum))
{
continue;
}
int tempmin = k - j;
if (!hashpent.Contains(tempmin))
{
continue;
}
if (tempmin < min)
{
min = tempmin;
}
}
}
return(min);
}
public static long LongestCollatzSequence(int n)
{
SpecialSequences.generatecollatz(n);
int max = SpecialSequences.CollatzSequences.Values.Max();
return(SpecialSequences.CollatzSequences.FirstOrDefault(x => x.Value == max).Key);
}
public static int HighlyDivisibleTriangularNumber(int n)
{
List <long> triangles = SpecialSequences.triangularnumbers(n * n);
foreach (int triangle in triangles)
{
if (MiscFunctions.Divisors(triangle).Count() > n)
{
return(triangle);
}
}
return(0);
}
public static long TriangularPentagonalHexagonal(int n)
{
List <long> pentagon = SpecialSequences.pentagonalnumbers(n);
List <long> hexagon = SpecialSequences.hexagonalnumbers(n);
HashSet <long> penthash = new HashSet <long>(pentagon);
for (int i = 143; i < hexagon.Count; i++)
{
if (penthash.Contains(hexagon[i]))
{
return(hexagon[i]);
}
}
return(0);
}
public static int IntegerRightTriangles(int n)
{
List <List <int> > righttriangles = SpecialSequences.GenerateTriangles(n);
List <int> perimeters = new List <int>();
foreach (List <int> triangle in righttriangles)
{
if (triangle.Sum() <= 1000)
{
perimeters.Add(triangle.Sum());
}
}
var most = perimeters.GroupBy(i => i).OrderByDescending(grp => grp.Count())
.Select(grp => grp.Key).First();
return(most);
}
public static int OddComposite()
{
int comp = 0;
List <int> primes = PrimeFunctions.GeneratePrimes(10000);
HashSet <int> primeshash = MiscFunctions.ListToHash(primes);
List <int> squares = SpecialSequences.squares(1000);
HashSet <int> squareshash = MiscFunctions.ListToHash(squares);
int i = 3;
bool found = false;
while (comp == 0)
{
found = false;
i += 2;
if (primeshash.Contains(i))
{
continue;
}
for (int j = 0; j < primes.Count; j++)
{
if (primes[j] > i)
{
break;
}
for (int k = 0; k < squares.Count; k++)
{
if (squares[k] * 2 > i)
{
break;
}
if (primes[j] + (squares[k] * 2) == i)
{
found = true;
}
}
}
if (!found)
{
comp = i;
}
}
return(comp);
}
public static int CodedTriangleNumbers(string n)
{
int count = 0;
string str = FileFunctions.readfileintostring("Problem42");
str = str.Replace("/", "");
str = str.Replace("\"", "");
string[] arr = str.Split(',');
List <long> triangles = SpecialSequences.triangularnumbers(1000);
foreach (string word in arr)
{
if (triangles.Contains(MiscFunctions.UppercaseWordValue(word)))
{
count++;
}
}
return(count);
}
public static int NumberSpiralDiagonals(int n)
{
return(SpecialSequences.SpiralNumbers((n + 1) / 2).Sum());
}
public static int fibbonacciNumber(int n)
{
SpecialSequences.GenerateFibbonacciDigits(n);
return(SpecialSequences.fibbonaccisequence.Count + 1);
}