Divisor Count of 18

Example of Use of Divisor Counting Function

 * $\map {\sigma_0} {18} = 6$

where $\sigma_0$ denotes the divisor counting function.

Proof
From Divisor Counting Function from Prime Decomposition:
 * $\ds \map {\sigma_0} n = \prod_{j \mathop = 1}^r \paren {k_j + 1}$

where:
 * $r$ denotes the number of distinct prime factors in the prime decomposition of $n$
 * $k_j$ denotes the multiplicity of the $j$th prime in the prime decomposition of $n$.

We have that:
 * $18 = 2 \times 3^2$

Thus:

The divisors of $18$ can be enumerated as:
 * $1, 2, 3, 6, 9, 18$