Q:

countdown from large number

I'm working on a solution to the third exercise of project Euler, and I need to loop over the odd numbers below sqrt(600851475143.0).  But I can't subtract 2 from the number every time the loop iterates, it stays the same every time.  According to this answer that is due to how numbers are stored and that everything just above and everything under the decimal point is lost.  How do I solve this?  I need decimal numbers, so I can't use an int (which would not have been big enough anyway). 

A:

Since you're looking for odd numbers, and odd numbers are by definition integer, just use an appropriate integer type instead of floating-point maths.