MVP-VM (Model View Presenter - ViewModel) with Data Binding and BackgroundWorker in Windows Forms applications

using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.Globalization;
using System.Linq;
using System.Runtime.Serialization;

namespace DataBinding
{
    [DataContract]
    public class Solver
    {
        private int max;
        private HashSet<int> multiples;

        [DataMember(Name = "Seeds")]
        private PositiveIntegerSetCollection seeds = new PositiveIntegerSetCollection();

        [DataMember]
        public int Max
        {
            get
            {
                return this.max;
            }

            set
            {
                Contract.Requires(value > 0, "Max must be a positive integer.");
                this.max = value;
            }
        }

        public PositiveIntegerSetCollection Seeds
        {
            get { return this.seeds; }
        }

        [DataMember]
        public int? Answer { get; private set; }

        public void FindSumOfMultiplesOfSeedsBelowMax()
        {
            Contract.Requires(this.Max > 0, "Max must be assigned a positive integer before calling this function.");
            Contract.Requires(this.Seeds.Count > 0, "At least one seed needs to be added before calling this function.");

            this.Answer = null;
            this.multiples = new HashSet<int>();
            this.GetMultiples();
            this.GetSum();
        }

        protected virtual bool FirstArgIsMultipleOfSecondArg(int firstArg, int secondArg)
        {
            return firstArg % secondArg == 0;
        }

        private void GetSum()
        {
            try
            {
                this.Answer = this.multiples.Sum();
            }
            catch (OverflowException ex)
            {
                var msg = string.Format(
                    CultureInfo.CurrentCulture,
                    "The sum was greater than {0}.\nThis program can not handle numbers larger than that. Please try different set of values.", 
                    int.MaxValue);
                throw new OperationFailedException(msg, ex);
            }
            finally
            {
                this.multiples.Clear();
            }
        }

        private void GetMultiples()
        {
            foreach (var v in this.seeds)
            {
                this.GetMultiplesOf(v);
            }
        }

        private void GetMultiplesOf(int seed)
        {
            for (var i = 1; i < this.Max; i++)
            {
                if (this.FirstArgIsMultipleOfSecondArg(i, seed))
                {
                    this.AccumulateResults(i);
                }
            }
        }

        private void AccumulateResults(int value)
        {
            try
            {
                this.multiples.Add(value);
            }
            catch (OutOfMemoryException ex)
            {
                this.multiples.Clear();
                var msg = string.Format(
                    CultureInfo.CurrentCulture, 
                    "Out of memory. Too many multiples ({0}) found...\nPlease try different set of values.",
                    this.multiples.Count);
                throw new OperationFailedException(msg, ex);
            }
        }
    }
}