I'd be glad to answer that~~. Actually, I'm not familiar with the tools to paste formulas in the test, so the formulas here are not quit recognizable; For pi(xi)(L<=i<=R), that is x(L) * x(L+1) * x(L+2) ... * X(R) ,all in the parentheses are subscripts.. it is something like sigma(xi)(L<=i<=R), which equals x(L)+....+x(R) More formally, pi(xi) is the products of all x(i) which has the subscript between L and R; and for Gi. i have defined it above, just for convenience: Gi=k^(2^(i)); That is ,Gr=k^(2^(r))

Oops, yes, you are right. It should be (G(R+1)-1)/(G(L)-1). I'll correct it. Thanks.~