a1a2a2...a30 =a1^30*d^((1+30)*30/2) =a1^30*d^465 =2^30a3a6a9...a30 =a1^10*d^(2+5+8+...+29) =a1^10*d^((2+29)*10/2) =a1^10*d^155 =(a1^30*d^465)^(1/3) =(2^30)^(1/3) =2^10 =1024
1
