From: "Joe Wölfel" <joe@...>
Date: 2008-10-20T23:18:42+09:00
Subject: Re: Counting

Right, as per my caveat n must be divisible by d*2.   You can't  
divide 1000 by twelve.  But 996 is divisible by 12.   So you can use  
that for d instead for that particular case.  If you played around  
with remainders for a bit you could adjust the formula I gave to work  
for all cases.

The point is you go from linear time for all the iterative methods to  
constant time if you just work out a formula.  For very large numbers  
the iterative methods will take more time than you are willing to  
spend and perhaps never finish at all.

On 18 oct. 08, at 11:02, Craig Demyanovich wrote:

> The OP needs multiples of 2 and 6. Since all multiples of 6 are also
> multiples of 2, just checking for multiples of 6 suffices. However,  
> if d =
> 6, your two approaches don't produce the same result. For d = 6, they
> produce 83498 and 83166, respectively. 83166 is the correct answer, I
> believe.
>
> Regards,
> Craig