In the first verses of 29 suras, there are letters that do not have a word meaning. These letters are called "Initial Letters" and there are 14 kinds (7 pairs) combinations.
15:87 We have given you the seven pairs, and the great Quran.
The initial letters are the introduction verse of the 29 suras, and after some, it is stated that these letters are evidence/signs/miracles.
2:1 Alif, Lâm, Mim.
3:1 Alif, Lam, Mim.
7:1 Alif, Lam, Mim, Sad.
10:1 Alif, Lam, Ra. These are the proofs of this book of wisdom.
11:1 Alif, Lam, Ra. This is a scripture whose verses have been perfected, then elucidated. It comes from a Most Wise, Most Cognizant.
12:1 Alif, Lam, Ra. These are proofs of this profound scripture.
13:1 Alif, Lam, Mim, Ra. These are proofs of this scripture. What is revealed to you from your Lord is the truth, but most people do not believe.
14:1 Alif, Lam, Ra. Bir kitaptır. A scripture that we revealed to you, in order to lead the people out of darkness into the light - in accordance with the will of their Lord - to the path of the Almighty, the Praiseworthy.
15:1 Alif, Lam, Ra. These are proofs of this scripture; a profound Quran.
19:1 Kef, Ha, Ya, Ayn, Sad.
20:1 Ta, He.
26:1-2 Ta, Sin, Mim. These constitute proofs of this clarifying scripture.
27:1 Ta, Sin. These constitute proofs of the Quran; a profound scripture.
28:1-2 Ta, Sin, Mim. These onstitute proofs of this profound book.
29:1 Alif, Lam, Mim.
30:1 Alif, Lam, Mim.
31:1-2 Alif, Lam, Mim. These constitute proofs of this book of wisdom.
32:1 Alif, Lam, Mim.
36:1 Ya, Sin.
38:1 Sad. and the Quran that contains the proof.
40:1 Ha, Mim.
41:1 Ha, Mim.
42:1-2 Ha, Mim. Ayn, Sin, Qaf.
43:1 Ha, Mim.
44:1 Ha, Mim.
45:1 Ha, Mim.
46:1 Ha, Mim.
50:1 Qaf. And the glorious Quran.
*In the Quran, the singular word "verse/ayat" means "miracle/sign/proof"; that is, it does not mean "one verse of the Quran". The word of "verses/ayaat" in plural means both "miracles/signs/proofs" and "verses of the Quran.
Initial letters protect the suras literally. In a sura with initial letters; the letters in the combination are mentioned as much as 19 times in that sura. For example; the sum of the letters 'ya' and 'sin' in the 36th Sura with the letter combination "ya + sin" is 285 (19x15).
Some suras have the same combination; the total sum of letters in these suras is a multiple of 19. For example; the sum of the letters 'alif', 'lam' and 'ra' in the 10,11,12,14,15th suras is 9481 (19x499).
Some suras have initial letter, not initial letters. Suras with initial letter are linked to suras that contain a combination of their letter. For example; the counts of the 38th Sura with the initial letter 'sad' are calculated together with the 7th and 19th Suras containing the letter 'sad' in its combination. Similarly, the 50th Sura with the letter 'qaf' is calculated together with the 42nd sura containing the letter 'qaf' in its combination.
In addition, striking "letter games" were performed in some of the suras with initial letters. For example; 68th Sura has 'nun' initial letter and the prophet YouNus is mentioned as "sahibil hut" (friend of the fish) that do not contain the letter "nun" are used. Similarly, while Lot's people are mentioned as "Qavm of Lot" throughout the Quran; in the 50th Sura (which has initial letter "qaf"), the word "ikhvanu Lot" was used (which a word don't contain "qaf" letter.