3^9 * 7^9      

________   = 3^2 * 7^2= 49*9=441 

3^7 * 7^7

(3^9*〖(7^3)〗^3)/〖21〗^7 =(3^9*7^9)/〖21〗^7 =〖21〗^9/〖21〗^7 =〖21〗^2