public void Problem45()
{
HashSet <long> hh = new HashSet <long>(Sequences.HexagonalNumbers().Take(1000000));
HashSet <long> hp = new HashSet <long>(Sequences.PentagonalNumbers().Take(1000000));
hh.IntersectWith(hp);
var matching = hh.Where(h => h.IsTriangle()).ToArray();
if (matching.Last() != 1533776805)
{
throw new InvalidOperationException("Problem not solved correctly");
}
}