# Notation for “is divisible by”

Is there a standard way of writing $a$ is divisible by $b$ in mathematical notation?

From what I've search it seems that writing $a \equiv 0 \pmod b$ is one way? But also you can write $b \mid a$ as well (the middle character is a pipe)? And sometimes that pipe is replaced by $3$ vertical dots?

Or is there a way of writing $a$ is a multiple of $b$ which I think means the same thing?

EDIT: thanks for the answers, is there a way to extend this and write something like: $b \mid a$ when $a = k$

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I usually use $|$ – Belgi Apr 22 '12 at 12:48
The standard is $b\mid a$ whic is typeset "b \mid a" in TeX – Andrea Mori Apr 22 '12 at 12:54
@pedja, thanks but that article lists both options – Jonathan. Apr 22 '12 at 13:03
@PeterPhipps The spacing is different, compare $A|B$, $A\mid B$, $A\vert B$, $A\lvert B$ and $A\rvert B$ (edit: there actually are differences there in some fonts, even if those are not visible here). – dtldarek Apr 22 '12 at 13:17

I have seen the following:

• $b \mid a$ that is with $\LaTeX$ \mid
• $a = 0 \mod b$ that is with $\LaTeX$ \mod
• $a = 0 \pmod b$ that is with $\LaTeX$ \pmod
• $a \bmod b = 0$ that is with $\LaTeX$ \bmod
• $a \equiv 0\ (b)$
• $a \equiv_{b} 0$

and of course there is

• $a = bk$ for some $k \in \mathbb{Z}$

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Thanks for the list, a mod b = 0 makes the most sense to me. But b|a seems more for use in commentary? – Jonathan. Apr 22 '12 at 13:19
It depends on so many things that I can't tell you this or that way. For me there are three important factors: how often will I use it (more often means less symbols), do I need to use it "in chains" like $a = b = c = d \pmod n$ and do I need to use different $n$-s, e.g. $a \equiv_3 b \equiv_5 c \equiv_7 d$ (which may be confusing but sometimes is helpful). Still, the most important criterion of all is readability. – dtldarek Apr 22 '12 at 13:26

There is also " $a \in b\mathbb Z$ ".

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I often write that as b divides a

Notation:

$$b \mid a$$

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This is the standard way, in the specific meaning of compliance to international standards: ISO 80000-2, clause 2.7-17. Note that the vertical bar character used there is normatively identified as U+2223 DIVIDES (∣), note the common U+007C VERTICAL LINE (|) that we enter directly on a keyboard. It is of course possible to express the same thing using a congruence notation, but only for integers (not e.g. for polynomials). – Jukka K. Korpela Jun 22 '12 at 5:09

Alexander Merkurjev taught me a long time ago the ingenious Russian notation $6 \vdots 2$, which I immediately adopted .
It pleasantly "rhymes" with the equivalent $(6)\subset (2)$

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I wonder if you are the unique non-Russian who uses that notation. I didn't think it is used in public outside of Russia (or at least Eastern Europe). – KCd Jan 22 '13 at 13:48

$a \equiv 0 \mod b$ and $b \mid a$ are both common, and their use depends on the context. Given a choice, I use the latter more than the former.

There are others such as $\text{lcm}(a,b)=a$ or $\text{hcf}(a,b)=b$ [or perhaps $\text{gcd}(a,b)=b$ if you prefer] which might also be used when more suitable for the context.

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