using System.Collections.Generic;
using System.Numerics;

namespace Algorithms.Sequences;

/// <summary>
///     <para>
///         Sequence of factorial numbers.
///     </para>
///     <para>
///         Wikipedia: https://en.wikipedia.org/wiki/Factorial.
///     </para>
///     <para>
///         OEIS: https://oeis.org/A000142.
///     </para>
/// </summary>
public class FactorialSequence : ISequence
{
    /// <summary>
    ///     Gets sequence of factorial numbers.
    /// </summary>
    public IEnumerable<BigInteger> Sequence
    {
        get
        {
            var n = 0;
            var factorial = new BigInteger(1);
            while (true)
            {
                yield return factorial;
                n++;
                factorial *= n;
            }
        }
    }
}