Learn Hardcore Indonesian: Saya menulis nomor itu dengan pulpen hitam, bukan pensil. - I write that number with a black pen, not a pencil.

Saya menulis nomor itu dengan pulpen hitam, bukan pensil. = not a pencil (but a pen). Use tidak to negate verbs, adjectives, or whole clauses.
Saya tidak menulis nomor itu. = I did not write that number. Even if you repeat the preposition, you still use bukan: ..., bukan dengan pensil.

Why is itu after nomor? Could I say itu nomor?

Demonstratives come after the noun by default in Indonesian: nomor itu, orang itu, rumah ini. Saying itu nomor isn’t the normal noun phrase order. You can put itu at the start only for topicalization or as a separate clause:

Itu nomor yang saya tulis... (That’s the number I wrote...)
Nomor itu saya tulis... (That number, I wrote...)

Why is hitam placed after pulpen?

Adjectives usually follow the noun: pulpen hitam (black pen), kucing putih (white cat). If you want to treat color as a noun phrase, you can say pulpen warna hitam or pulpen berwarna hitam, but you wouldn’t normally say hitam pulpen in a noun phrase. As a clause, you can say: Pulpen itu hitam.

Do I need the comma before bukan pensil?

It’s optional but common, because you’re marking a contrast (“not X but Y”). Without the comma it’s still correct. You can also use a fuller contrast:

..., bukan pensil melainkan pulpen hitam.
..., bukan dengan pensil.

Do I have to repeat dengan in the second part: ..., bukan dengan pensil?

No. It’s fine (and common) to omit the repeated preposition after bukan: ..., bukan pensil. Repeating dengan is also acceptable for clarity or emphasis.

What’s the difference between pulpen, pena, and bolpoin/bolpen?

pulpen: everyday word for “pen,” often understood as a ballpoint in practice.
pena: neutral/standard “pen,” sometimes feels a bit more formal or literary.
bolpoin/bolpen: specifically “ballpoint pen.” All are widely understood; usage varies by region and register.

What’s the difference between nomor, angka, and bilangan?

nomor: a label/identifier (room number, license plate, phone number). That’s what fits the sentence: nomor itu = that specific number/identifier.
angka: digit(s)/numerals or figures/statistics (e.g., angka 7, angka kematian).
bilangan: mathematical “number” (more technical/educational term).

Could I say menuliskan instead of menulis here?

Yes, but nuance shifts. Menulis is the neutral “to write.” Menuliskan can add a sense of writing something down for someone or onto something (causative/applicative feel), or it foregrounds the object:

Saya menuliskan nomor itu di papan. (I wrote that number on the board.) In your sentence, menulis is perfectly natural; menuliskan is also acceptable but slightly heavier.

What’s happening morphologically in menulis? Why not mentulis?

The verb root is tulis. The active prefix meN- assimilates to the first consonant of the root:

Before t, the t drops and you get men-
- ulis → menulis (not mentulis). Other examples:
baca → membaca, kirim → mengirim, sapu → menyapu, catat → mencatat.

Is Saya the best choice here? What about aku or gue?

saya: polite/neutral; safe in most contexts, especially with strangers or in formal settings.
aku: informal/intimate; with friends/family or informal writing.
gue: very informal, Jakarta/urban slang. Pick based on relationship and formality. The rest of the sentence doesn’t need to change.

Is dengan the only way to say “with/using” here?

No. Common alternatives:

pakai (colloquial): Saya menulis nomor itu pakai pulpen hitam.
memakai or menggunakan (more formal): Saya menulis nomor itu menggunakan pulpen hitam. You typically need a preposition or a verb like pakai; you can’t just drop it: ✗ Saya menulis nomor itu pulpen hitam.

If I drop itu, how does the meaning change?

Nomor itu = that specific number (definite).
Nomor (without itu) = a number (non-specific/indefinite). So you’d be stating you wrote some number, not a particular one already known to speaker/listener.

Can I say nombor instead of nomor?

nombor is standard Malay (Malaysia/Brunei). In Indonesian (Indonesia), the standard spelling is nomor. You may hear nomer colloquially in some regions, but nomor is the standard.

Is pensil spelled with a c like in English?

No. Indonesian spells it pensil, with an s. Pronunciation roughly matches the spelling; don’t write pencil in Indonesian.

Can I say Saya bukan menulis nomor itu... to mean “I didn’t write that number”?

Not for a simple negation. To negate the verb, use tidak: Saya tidak menulis nomor itu.
Bukan + verb phrase is used for contrastive correction like “It’s not that I wrote the number, (but rather I did X),” which is a different meaning.

How do I abbreviate nomor in writing?

You’ll often see No. (with a period) before an identifying number: No. 12, No. Telepon. In informal contexts, people also write No without a period or just use no in phrases like no HP (phone number), but No. is the safe, conventional form.