Trello.cs

public class Trello
{
    public String Letters { get; set; }

    public Int64 InitialHash { get; set; }
    public Int64 Hash { get; set; }
    public Int64 HashDepth { get; set; }

    public Trello(String letters, Int64 initialHash, Int64 hashDepth)
    {
        this.Letters = letters;
        this.InitialHash = initialHash;
        this.Hash = this.InitialHash;
        this.HashDepth = hashDepth;
    }

    public Trello()
        : this(
                "acdegilmnoprstuw", // Letters
                7,                  // InitialHash
                37                  // HashDepth
        )
    { }

    /// <summary>
    /// Get the hashcode of "s" (parameter)
    /// </summary>
    /// <param name="s"></param>
    /// <returns></returns>
    public Int64 GetHashCode(String s)
    {
        foreach (var item in s)
        {
            this.Hash = (this.Hash * this.HashDepth + this.Letters.IndexOf(item));
        }
        return this.Hash;
    }

    /// <summary>
    /// Get the initial string of hashCode
    /// </summary>
    /// <param name="hashCode"></param>
    /// <returns></returns>
    public String ReverseHashCode(Int64 hashCode)
    {
        var reversed = "";

        while (hashCode > this.InitialHash)
        {
            var index = hashCode % this.HashDepth;
            var charValue = this.Letters[(int)index];
            reversed += charValue;
            hashCode = (hashCode - index) / this.HashDepth;
        }

        var x = "";
        for (int i = 0; i < reversed.Length; i++)
        {
            x += reversed[reversed.Length - 1 - i];
        }
        return x;
    }
}