public static IEnumerable <long> GetAbundantNumbers(long limit)
{
return
(Sequences.LongRange(1, limit)
.Select(n => new Tuple <long, HashSet <long> >(n, Problem012.GetFactors(n)))
.Where(t => t.Item1 < t.Item2.Sum() - t.Item1) // subtract t.Item1 to get only proper divisors
.Select(t => t.Item1));
}
public string Solve()
{
var result = Enumerable.Range(2, 9998).Select(n =>
{
// may want to refactor GetFactors to return a copy...
var factors = Problem012.GetFactors(n);
// get n, sum of factors of n
return(Tuple.Create((long)n, factors.Sum() - n));
}).Where(n =>
{
// remove self-amicable numbers (6, 496, 8128)
if (n.Item1 == n.Item2)
{
return(false);
}
var factors = Problem012.GetFactors(n.Item2);
// do the sum of the factors of (the sum of the factors of n) equal n?
return(n.Item1 == (factors.Sum() - n.Item2));
}).Select(n => n.Item1).Distinct();
return(result.Sum().ToString());
}