Math
posted by Jack .
I don't have any specific problems I need help with, but I'm a bit confused about two things:
1) Where 2^x  1 = y, is x or y the Mersenne prime?
2) I have noticed that in some cases, such as 27 * 3, I can break the problem up and arrive at the correct result:
27 * 3 = 81
(20 * 3) + (7 * 3) = 60 + 21 = 81
Does this work in all cases? I'm having trouble finding a problem that isn't correctly solved this way, but in the past I have tried this and arrived at the wrong answer. Does anyone know how this works?

2) it works in all cases.
(a+b)c=a*c + b*c is why this is true.
1) y is the Mersenne Prime. And, big news in that area, the first 44 are now known.
http://www.mersenne.org/ 
I see, thanks. I must have been doing it wrong when it didn't work.