There are several variants of the notation for multiplication:
- $n \times m$
This is usually used when numbers are under consideration, for example: $3 \times 5 = 15$.
However, it can be used in the context of algebra where extra clarity is needed.
- $n m$
- $\paren n \paren m$
- $n \cdot m$ or $n . m$
- $n * m$
This notation specifically evolved in the field of computer science, but can occasionally be seen encroaching into mathematics.
Its use is not recommended, as it can be confused with other operations that use the same or similar notation, for example convolution.