a) aaa = 100a + 10a + a = 111a = 3 x 37a divizibil cu 3
b) ababab = 100000a + 10000b + 1000a + 100b + 10 a + b = 101010a + 10101b = 33670a x 3 + 3367b x 3 = 3(33670a + 3367b) divizibil cu 3
c) bbbaaa = 100000b + 10000b + 1000b + 100a + 10a + a = 111000b + 111a =
37000b x 3 + 37a x 3 = 3(37000b + 37a) divizibil cu 3