ASP MVC code first create computed primary key

I am using code first in asp mvc and i came across a situation where i need to have a model/table with a computed primary key for example:

 public class Student
{
    [Key]
    public string StudentNumber { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public DateTime RegistrationDate { get; set; }

}

So is there a way to make the StudentNumber to be computed by for example taking 1st letter of the LastName, the year of registration and an autoincrement number?

For performance reasons, you really don't want to have your primary key as a string, so question where this requirement is coming from. However:

[Key]
public int Id { get; set; }

[NotMapped]
public string StudentId 
{ 
    get 
    { 
        return string.Format("{0}{1}{2}", 
            this.LastName.Substring(0, 1), 
            this.RegistrationDate.Year,
            this.Id);
    }
}