الرقم ألف.

A careful full reading in MSA is:

ar-raqmu alfun

A common pause form, which is how people often actually stop at the end of a sentence, is:

ar-raqm alf

A few pronunciation notes:

• الرقم begins with al-, but because ر is a sun letter, it is pronounced ar-, not al-.
• The ق in رقم is qāf, a deep back-of-the-throat q sound, not an English k.
• ألف begins with a clear hamza: ʾalf.

Because Arabic often uses a nominal sentence in the present tense without an explicit verb to be.

So:

• الرقم ألف literally looks like the number one thousand
• but it means The number is one thousand

This is completely normal in Arabic.
If you wanted was, will be, and so on, then Arabic would usually use a verb.

This happens because ر is a sun letter.

In Arabic, when ال comes before a sun letter, the l sound is not pronounced, and the next consonant is doubled.

So:

• written: الرقم
• pronounced: ar-raqm / ar-raqmu

The spelling does not change, only the pronunciation.

If you add the full case endings, the sentence is:

الرَّقْمُ أَلْفٌ

This is because:

• الرَّقْمُ is the subject/topic of the nominal sentence, so it is nominative
• أَلْفٌ is the predicate, and it is also nominative

In normal unvoweled writing, those endings are usually not shown, so you just see:

الرقم ألف

And in pause, speakers often stop with:

• ar-raqm
• alf

instead of fully pronouncing ar-raqmu alfun.

Because it is the predicate and it is indefinite here.

The structure is:

• الرقم = the number → definite
• ألف = one thousand / a thousand → indefinite

So the sentence means that the thing identified as the number has the value one thousand.

If you said الألف, that would mean the thousand or possibly the alif, depending on context, which is a different idea.

In context, الرقم can be translated as number, digit, or numeral, depending on what is being discussed.

Here, the most natural English meaning is simply the number.

A useful nuance:

• رقم often refers to a written number, numeral, digit, figure, or number label
• عدد more often refers to quantity or number in a counting sense

But in many everyday contexts, English learners can safely understand الرقم here as the number.

Yes, it is the same spelling: ألف.

But context tells you the meaning.

It can mean:

• one thousand
• the name of the Arabic letter alif

In this sentence, because the meaning is already given and because it follows الرقم, it means one thousand, not the letter name.

Because Arabic nominal sentences usually begin with the topic/subject and then give information about it.

So the pattern is:

• الرقم = the topic: the number
• ألف = the comment/predicate: one thousand

That makes الرقم ألف a very natural structure.

If you reverse the words, you would change the structure and probably the meaning or make it sound unnatural in this simple context.

You could write:

الرقم ١٠٠٠

That means the same thing as:

الرقم ألف

Arabic often allows either:

• the number written out in words
• or written with numerals

In careful formal MSA, you can pronounce them:

ar-raqmu alfun

But in most real-life speech, many speakers drop the final case endings, especially at pause, and say something closer to:

ar-raqm alf

So:

• with endings = more formal, careful, textbook-style, recitation-style
• without endings = very common in actual speech

If you are learning MSA, it is good to know the full endings even if you do not always pronounce them in conversation.