Elementary Algebra

$3\times3\times17$
Since the sum of the digits of $153$ is $9$, which is a multiple of $9$, this number is divisible by $9$. When we divide $153$ by $9$, we get $17$. The number $9$ can further be broken down into prime factors: $3\times3$. Since $3$ and $17$ are both prime numbers, the prime factorization of $153$ is $3\times3\times17$