3 x 7 = 21 You can put "to the first power" after the three and the seven, but it's not necessary.
The prime factorization of 50 using exponents is 21 x 52
3 x 7 = 21 No exponents necessary.
3 x 7 = 21
10 = 21*51
21 x 33
It is: 21*52 = 50
250 = 21 x 53
21 x 831 = 166
It is: 21*71*111 = 154
1250 = 21 x 54
54 = 21 x 33
18 = 21 x 32