1 , 72 , 21 = 21-7=143 , 35 = 35-21=144 , 49 = 49-35=145 , 63 = 63-49=146 , 777 = 77+14=91望采纳
1(7x1)=72(7x3)=213(7x5)=354(7x7)=495(7x9)=636 (7x11)=777 (7x13)=91
91望采纳谢谢