God informs us in Chapter 74 that the authenticity of the Quran will be proven by the number 19.
Verse 35 describes this 19-based mathematical code as "One of the great miracles":

Chapter 74 - The Hidden Secret

Over it is nineteen.

Absolutely, (I swear) by the moon.
And the night as it passes.
And the morning as it shines. This is one of the great miracles.

Basic Facts:

The Quran consists of 114 chapters, which is 19 x 6.

The total number of verses in the Quran is 6346, or 19 x 334.
Note that 6 + 3 + 4 + 6 = 19.

The word "God" (Allah) occurs in the Quran 2698 times,
and this number equals 19 x 142.

The total sum of verse numbers for all verses containing the word
"God" is 118123, also a multiple of 19 (118123 = 19x6217).

"The Quran" is mentioned in the Quran 57 times, 19 x 3.

The first verse, known as "Basmalah," consists of 19 letters.

The word "proof" is written throughout the entire Quran 19 times.

The famous first revelation (96:1-5) consists of 19 words.

This 19-worded first revelation consists of 76 letters, or 19 x 4.

The first chapter revealed (Sura 96) consists of 19 verses.

This first chapter revealed is placed atop the last 19 chapters.

This chapter also consists of 304 letters, or 19 x 16.

The last revelation (Sura 110) consists of 19 words.

The first verse of the last revelation (110:1) consists of 19 letters.

The Quran mentions 30 different numbers: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 19, 20, 30, 40, 50,
60, 70, 80, 99, 100, 200, 300, 1000, 2000, 3000, 5000, 50,000, & 100,000.
The sum of these numbers is 162146, which equals 19x8534.

Superhuman Mathematical Design

Now that we have grasped a few of the basic facts, let us examine the truly
miraculous design of the mysterious "Quranic Initials":

Chapter 10: A. L. R. These (letters) are the proofs of this book of wisdom.

Chapter 28: T. S. M. These (letters) constitute proofs of this profound book.

Chapter 38: S., and the Quran that contains the proof.