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 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);
}
