An index is sometimes called a power or an exponent.
In 54, the 4 is the index and the 5 is the base.
54 is read as "5 to the power 4" or "5 to the 4" and means 5 x 5 x 5 x 5.
Dividing numbers
When we divide numbers with the same base number, we can just subtract the indices.
57 ÷ 53 = 54
This is because, when we divide we can cancel a 5 on the top with a 5 on the bottom, leaving four 5s on the top.
