According to the Fundamental Theorem of Arithmetic, every integer greater than 1 is either prime or a product of primes and that product is unique.
The prime factorization of 8=2×2×2
No other number can have the same prime factorization.
Decimal expansion can be understood by taking an example.
eg- 0.1234 can be written as (110)+(2100)+(31000)+(410000)