how to make this in prolog

From: raf_go (raf_go_at_go2.pl)
Date: 03/25/04 

Date: Thu, 25 Mar 2004 18:08:32 +0100

I nead make somthink like that in prolog

x=1;
y=2;

for(...){
a= 2^x * (2^y - 1);
x+=1;
y+=1;
}

for help thanks.