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:

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

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: Fermat
• 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): semiprime