Generator wow... spicy!!!!

I tried to calc the 2n term directly from the cloused form formula but the numbers are too big for the standar float, and
are too big too for a reasonable precision of the decimal module. I tested some numbers and the calculation get too long
before getting the needed precision.

So the best way is using int. I did a raw for for it. The interesting of this solution is the use of a generator that improve the readability a lot.