# Definition:Semiprime Number

## Definition

A **semiprime (number)** is an integer which is the product of two (not necessarily distinct) primes.

### Sequence

The sequence of **semiprimes** begins:

- $4, 6, 9, 10, 14, 15, 21, 22, 25, 26, 33, 34, 35, 38, 39, 46, 49, 51, 55, 57, \ldots$

This sequence is A001358 in the On-Line Encyclopedia of Integer Sequences (N. J. A. Sloane (Ed.), 2008).

## Examples

Obvious examples: if $p, p_1, p_2$ are prime, then:

- $p^2$ is
**semiprime**. - $2 p$ is
**semiprime**. - $p_1 p_2$ is
**semiprime**.

## Also known as

A **semiprime number** is most usually referred to just as a **semiprime**.

The additional specifier **number** has been included in its name on $\mathsf{Pr} \infty \mathsf{fWiki}$ so as to provive a convenient means of disambiguation from other objects whose names include the term **semiprime**.

Some sources refer to a **semiprime** as an **almost-prime**.

Some sources hyphenate: **semi-prime**.

## Also see

- Results about
**semiprimes**can be found here.

## Sources

- 1986: David Wells:
*Curious and Interesting Numbers*... (previous) ... (next): $33$ - 1997: David Wells:
*Curious and Interesting Numbers*(2nd ed.) ... (previous) ... (next): $33$ - 2008: Ian Stewart:
*Taming the Infinite*... (previous) ... (next): Chapter $7$: Patterns in Numbers