>>>>
>>>>Off topic but since I think you enjoy obscure code I just wrote this (purely as a mockup):

static IEnumerable<int> GetSequence()
>>>>        {
>>>>            bool b = false;
>>>>            int x1 = 0;
>>>>            int x2 = 1;
>>>>
>>>>            while (true)
>>>>            {
>>>>                b=!b;
>>>>                yield return b ? x1 += x2 : x2 += x1;
>>>>            }
>>>>        ]

>>>
>>>working my way through it with a pencil
>>>
>>>1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
>>>
>>>
>>>If we number them as n0, n1, n2, n3, n4, ....
>>>
>>>then n[i] = n[i-1] + n[i-2]
>>
>>yep. Next in the series is the sum of the previous two items. It's called the Fibonacci series - but I actually got it wrong. It should be:
>>0,1,1,2,3,5,8 etc
>
>
>Take -1 as starting value for x1
>
>

>  int x1 = -1;
>  int x2 = 1;
>

That would do it.

>As an alternative, you can do the calculation after the yield return

Messier :-}
Actually all I really needed for testing was *any* sequence of ints - just thought I do this to make it more interesting.....