الرقم مليون.

In Arabic, the present tense of to be is usually not stated in simple sentences like this.

So:

• الرقم مليون literally looks like the number one million but it means The number is one million.

This is called a nominal sentence in Arabic.
If you wanted past tense, you would usually add a verb, for example:

• كان الرقم مليونًا = The number was one million.

الرقم means the number.

It comes from the noun رقم = number.
The prefix الـ is the Arabic definite article, meaning the.

So:

• رقم = a number
• الرقم = the number

Because مليون is functioning like the predicate of the sentence: it tells you what the number is.

In Arabic nominal sentences, the first noun is often definite and the second part is often indefinite:

• الرقم مليون = The number is one million

If you said المليون, that would mean the million, which usually would not fit this sentence naturally.

So the pattern is:

• الرقم = the subject, definite
• مليون = the predicate, indefinite

In Arabic, مليون by itself already means one million in most contexts.

So:

• مليون = one million / a million

You normally do not say واحد مليون for standard counting.
Adding واحد here would sound unnatural in Modern Standard Arabic.

Compare:

• مليون = one million
• مليونان = two million
• ثلاثة ملايين = three million

A common careful pronunciation is:

• ar-raqmu milyūn

A few notes:

• الرقم is pronounced ar-raqm because the ل in الـ assimilates before ر
• مليون is pronounced roughly milyoon

If full case endings are pronounced in formal reading, you may hear:

• ar-raqmu milyūnun

But in everyday careful speech, many speakers drop final case vowels, so:

• ar-raqm milyūn

is also common in practice.

In fully inflected MSA, the sentence would usually be:

• الرَّقْمُ مِلْيُونٌ

Here is why:

• الرَّقْمُ takes ـُ because it is the subject of the nominal sentence
• مِلْيُونٌ takes ـٌ because it is the predicate and indefinite

So grammatically:

• الرَّقْمُ = nominative definite noun
• مِلْيُونٌ = nominative indefinite predicate

In less formal writing, these endings are usually omitted.

It is grammatically understandable, but context matters.

الرقم مليون is a straightforward equational sentence meaning The number is one million. It can work, especially in exercises or very direct statements.

Depending on context, Arabic might also use other expressions, such as:

• العدد مليون = The number is one million
• قيمته مليون = Its value is one million
• الرقم هو مليون = The number is one million

The version with هو adds emphasis or clarity, but it is not required.

Both can relate to number, but they are used a bit differently.

• رقم often means a numeral, figure, number label, digit, number used as an identifier
• عدد often means quantity or number in the mathematical/counting sense

Examples:

• رقم الهاتف = phone number
• عدد الطلاب = the number of students

In your sentence, الرقم مليون is understandable, but in some contexts العدد مليون may sound more like the quantity is one million.

Yes, you can.

• الرقم مليون = The number is one million
• الرقم هو مليون = The number is one million

The word هو here is a pronoun used as a separator/emphasis device in some nominal sentences. It can make the structure feel clearer, especially for learners.

However, in a simple sentence like this, هو is not necessary.

You can keep the same structure:

• الرقم ألف = The number is one thousand
• الرقم مليون = The number is one million
• الرقم مليار = The number is one billion

For other quantities:

• الرقم مليونان = The number is two million
• الرقم ثلاثة ملايين = The number is three million
• الرقم عشرة ملايين = The number is ten million

So the sentence pattern stays the same; only the number expression changes.

It is a borrowed word that has become standard in Arabic.

مليون is widely used in Modern Standard Arabic and everyday Arabic for million. Even though it is not from an old Arabic root in the same way many native Arabic words are, it is completely normal and standard today.