Recursos da avaliação do .NET

                using System.Collections.Generic;

namespace FibonacciTest
{
    public static class FibonacciGenerator
    {
        public static IEnumerable<int> Fibonacci()
        {
            int current = 1, next = 1;
            while (true)
            {
                yield return current;
                next = current + (current = next);
            }
        }
    }
}