cho a=1+3+3^2+3^3+3^4+.....+3^7 :Tuzki25:Tuzki25:Tuzki25:Tuzki25:Tuzki25 :Rabbit39:Rabbit39:Rabbit39:Rabbit39:Rabbit39:Rabbit39 :Chuothong4:Chuothong4:Chuothong4:Chuothong4:Chuothong4:Chuothong4